diff --git a/NEXT-STEPS.md b/NEXT-STEPS.md
index 7d2efb2..d8b1f52 100644
--- a/NEXT-STEPS.md
+++ b/NEXT-STEPS.md
@@ -65,66 +65,81 @@ That turns the simulation into a real strategy loop.
 2. Make pirate target selection explicitly prefer economic targets.
 3. Surface faction stocks, throughput, and build priorities in the HUD/debug views.
 4. Expand the order/behavior set with higher-value RTS actions like `hold-here`, `attack`, and `defend-area`.
-5. Break [src/game/GameApp.ts](/home/jbourdon/repos/space-game/src/game/GameApp.ts) into smaller planning / faction / combat / logistics modules.
+5. Break backend simulation responsibilities into smaller planning / faction / combat / logistics modules.
 
-## Migration To .NET
+## Network / Multiplayer
 
-If the long-term goal is multiplayer, scale, persistence, or server authority, a .NET migration is a sensible next architectural track.
+The repository now has a split architecture:
 
-Recommended direction:
+- [apps/backend](/home/jbourdon/repos/space-game/apps/backend)
+  - authoritative .NET simulation
+- [apps/viewer](/home/jbourdon/repos/space-game/apps/viewer)
+  - rendering and observer UI
+- `GET /api/world`
+  - initial snapshot
+- `GET /api/world/stream`
+  - incremental SSE delta stream
 
-- keep the current Vite / Three.js client for rendering and input
-- move simulation authority into a .NET backend
-- treat the browser client as a renderer + command UI
+The next networking step is not “move the simulation into .NET.” That is already done for the active runtime.
 
-Suggested migration phases:
+The next steps are about scaling the transport and authority model cleanly.
 
-1. Define a shared simulation contract.
-   - ship state snapshots
-   - orders
-   - behaviors
-   - assignments
-   - combat / economy events
+Recommended work:
 
-2. Extract the pure simulation model from the Three.js runtime.
-   - separate rendering state from simulation state
-   - remove direct scene dependencies from game logic
+- add client-to-server command submission
+  - direct orders
+  - automation changes
+  - selection / observer commands only where useful
+- add persistence
+  - saves
+  - world seeds
+  - reconnect support
+- add player ownership / permissions
+  - command authority
+  - eventually fog of war / restricted information
+- harden replication contracts
+  - explicit entity lifecycle events
+  - versioning
+  - reconnect / catch-up semantics
 
-3. Rebuild the simulation core in .NET.
-   - `Order`
-   - `DefaultBehavior`
-   - `Assignment`
-   - `ControllerTask`
-   - faction economy
-   - combat resolution
+## Interest Management
 
-4. Add server-driven ticking.
-   - authoritative world step on the server
-   - deterministic or near-deterministic update model
-   - event stream / snapshot replication to clients
+The current stream is world-wide.
 
-5. Add persistence and multiplayer infrastructure.
-   - saves
-   - world seeds
-   - reconnect support
-   - eventually player ownership / fog / permissions
+That means every observer receives deltas for the full simulation, even when only looking at one part of space.
 
-Suggested .NET stack:
+Recommended work:
 
-- ASP.NET Core for API / realtime transport
-- SignalR or custom websocket layer for simulation updates
-- PostgreSQL for persistence
-- background hosted service for world ticks
+- add observer/view-scoped subscriptions
+  - visible systems
+  - nearby ships / stations / nodes
+  - faction-scoped or player-scoped channels later
+- support subscribe / unsubscribe as camera focus changes
+- send only relevant deltas per observer
+- keep coarse strategic updates available for off-screen context
+  - system ownership
+  - major combat
+  - economy summaries
 
-Suggested immediate prep before migration:
+This is the key step that makes many simultaneous observers practical without broadcasting the entire world to everyone.
 
-- isolate simulation data structures from rendering objects
-- isolate faction AI from UI code
-- isolate travel / docking / mining / combat systems into separate modules
-- make event emission explicit and serializable
+## Replication Quality
 
-The key rule for the migration is:
+The backend already sends:
 
-- do not port Three.js-shaped code into .NET
-- first separate the simulation from rendering in TypeScript
-- then move the pure simulation into .NET cleanly
+- initial snapshot
+- incremental deltas
+- event records
+
+Recommended work:
+
+- add stronger event typing
+  - spawn
+  - destroy
+  - dock
+  - undock
+  - cargo transfer
+  - combat hit / kill
+- improve interpolation and extrapolation policies per entity type
+- add resync handling when a client falls too far behind
+- consider switching from SSE to websocket transport if bidirectional command traffic becomes heavy
diff --git a/apps/backend/Contracts/WorldContracts.cs b/apps/backend/Contracts/WorldContracts.cs
index 3ca2a3a..da0cee2 100644
--- a/apps/backend/Contracts/WorldContracts.cs
+++ b/apps/backend/Contracts/WorldContracts.cs
@@ -3,6 +3,8 @@ namespace SpaceGame.Simulation.Api.Contracts;
 public sealed record WorldSnapshot(
   string Label,
   int Seed,
+  long Sequence,
+  int TickIntervalMs,
   DateTimeOffset GeneratedAtUtc,
   IReadOnlyList<SystemSnapshot> Systems,
   IReadOnlyList<ResourceNodeSnapshot> Nodes,
@@ -10,6 +12,24 @@ public sealed record WorldSnapshot(
   IReadOnlyList<ShipSnapshot> Ships,
   IReadOnlyList<FactionSnapshot> Factions);
 
+public sealed record WorldDelta(
+  long Sequence,
+  int TickIntervalMs,
+  DateTimeOffset GeneratedAtUtc,
+  bool RequiresSnapshotRefresh,
+  IReadOnlyList<SimulationEventRecord> Events,
+  IReadOnlyList<ResourceNodeDelta> Nodes,
+  IReadOnlyList<StationDelta> Stations,
+  IReadOnlyList<ShipDelta> Ships,
+  IReadOnlyList<FactionDelta> Factions);
+
+public sealed record SimulationEventRecord(
+  string EntityKind,
+  string EntityId,
+  string Kind,
+  string Message,
+  DateTimeOffset OccurredAtUtc);
+
 public sealed record SystemSnapshot(
   string Id,
   string Label,
@@ -33,6 +53,14 @@ public sealed record ResourceNodeSnapshot(
   float MaxOre,
   string ItemId);
 
+public sealed record ResourceNodeDelta(
+  string Id,
+  string SystemId,
+  Vector3Dto Position,
+  float OreRemaining,
+  float MaxOre,
+  string ItemId);
+
 public sealed record StationSnapshot(
   string Id,
   string Label,
@@ -45,6 +73,18 @@ public sealed record StationSnapshot(
   float RefinedStock,
   string FactionId);
 
+public sealed record StationDelta(
+  string Id,
+  string Label,
+  string Category,
+  string SystemId,
+  Vector3Dto Position,
+  string Color,
+  int DockedShips,
+  float OreStored,
+  float RefinedStock,
+  string FactionId);
+
 public sealed record ShipSnapshot(
   string Id,
   string Label,
@@ -52,6 +92,28 @@ public sealed record ShipSnapshot(
   string ShipClass,
   string SystemId,
   Vector3Dto Position,
+  Vector3Dto Velocity,
+  Vector3Dto TargetPosition,
+  string State,
+  string? OrderKind,
+  string DefaultBehaviorKind,
+  string ControllerTaskKind,
+  float Cargo,
+  float CargoCapacity,
+  string? CargoItemId,
+  string FactionId,
+  float Health,
+  IReadOnlyList<string> History);
+
+public sealed record ShipDelta(
+  string Id,
+  string Label,
+  string Role,
+  string ShipClass,
+  string SystemId,
+  Vector3Dto Position,
+  Vector3Dto Velocity,
+  Vector3Dto TargetPosition,
   string State,
   string? OrderKind,
   string DefaultBehaviorKind,
@@ -73,4 +135,14 @@ public sealed record FactionSnapshot(
   int ShipsBuilt,
   int ShipsLost);
 
+public sealed record FactionDelta(
+  string Id,
+  string Label,
+  string Color,
+  float Credits,
+  float OreMined,
+  float GoodsProduced,
+  int ShipsBuilt,
+  int ShipsLost);
+
 public sealed record Vector3Dto(float X, float Y, float Z);
diff --git a/apps/backend/Program.cs b/apps/backend/Program.cs
index 93466bf..a30dd5e 100644
--- a/apps/backend/Program.cs
+++ b/apps/backend/Program.cs
@@ -1,6 +1,8 @@
 using SpaceGame.Simulation.Api.Simulation;
+using System.Text.Json;
 
 var builder = WebApplication.CreateBuilder(args);
+var sseJsonOptions = new JsonSerializerOptions(JsonSerializerDefaults.Web);
 
 builder.WebHost.UseUrls("http://127.0.0.1:5079");
 builder.Services.AddCors((options) =>
@@ -22,10 +24,30 @@ app.UseCors();
 
 app.MapGet("/", () => Results.Redirect("/api/world"));
 app.MapGet("/api/world", (WorldService worldService) => Results.Ok(worldService.GetSnapshot()));
+app.MapGet("/api/world/stream", async (HttpContext httpContext, WorldService worldService, CancellationToken cancellationToken) =>
+{
+  httpContext.Response.Headers.Append("Cache-Control", "no-cache");
+  httpContext.Response.Headers.Append("Content-Type", "text/event-stream");
+
+  var afterSequenceRaw = httpContext.Request.Query["afterSequence"].ToString();
+  _ = long.TryParse(afterSequenceRaw, out var afterSequence);
+  var stream = worldService.Subscribe(afterSequence, cancellationToken);
+
+  await httpContext.Response.WriteAsync(": connected\n\n", cancellationToken);
+  await httpContext.Response.Body.FlushAsync(cancellationToken);
+
+  await foreach (var delta in stream.ReadAllAsync(cancellationToken))
+  {
+    var payload = JsonSerializer.Serialize(delta, sseJsonOptions);
+    await httpContext.Response.WriteAsync($"event: world-delta\ndata: {payload}\n\n", cancellationToken);
+    await httpContext.Response.Body.FlushAsync(cancellationToken);
+  }
+});
 app.MapGet("/api/world/health", (WorldService worldService) => Results.Ok(new
 {
   ok = true,
-  generatedAtUtc = worldService.GetSnapshot().GeneratedAtUtc,
+  sequence = worldService.GetStatus().Sequence,
+  generatedAtUtc = worldService.GetStatus().GeneratedAtUtc,
 }));
 app.MapPost("/api/world/reset", (WorldService worldService) =>
 {
diff --git a/apps/backend/Properties/launchSettings.json b/apps/backend/Properties/launchSettings.json
index c55f6a2..d49908c 100644
--- a/apps/backend/Properties/launchSettings.json
+++ b/apps/backend/Properties/launchSettings.json
@@ -4,7 +4,7 @@
     "http": {
       "commandName": "Project",
       "dotnetRunMessages": true,
-      "launchBrowser": true,
+      "launchBrowser": false,
       "applicationUrl": "http://localhost:0",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development"
@@ -13,7 +13,7 @@
     "https": {
       "commandName": "Project",
       "dotnetRunMessages": true,
-      "launchBrowser": true,
+      "launchBrowser": false,
       "applicationUrl": "https://localhost:0;http://localhost:0",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development"
diff --git a/apps/backend/Simulation/RuntimeModels.cs b/apps/backend/Simulation/RuntimeModels.cs
index f2868cb..8c0c051 100644
--- a/apps/backend/Simulation/RuntimeModels.cs
+++ b/apps/backend/Simulation/RuntimeModels.cs
@@ -13,6 +13,7 @@ public sealed class SimulationWorld
   public required List<ShipRuntime> Ships { get; init; }
   public required List<FactionRuntime> Factions { get; init; }
   public required Dictionary<string, ShipDefinition> ShipDefinitions { get; init; }
+  public int TickIntervalMs { get; init; } = 200;
   public DateTimeOffset GeneratedAtUtc { get; set; }
 }
 
@@ -30,6 +31,7 @@ public sealed class ResourceNodeRuntime
   public required string ItemId { get; init; }
   public float OreRemaining { get; set; }
   public float MaxOre { get; init; }
+  public string LastDeltaSignature { get; set; } = string.Empty;
 }
 
 public sealed class StationRuntime
@@ -43,6 +45,7 @@ public sealed class StationRuntime
   public float RefinedStock { get; set; }
   public float ProcessTimer { get; set; }
   public HashSet<string> DockedShipIds { get; } = [];
+  public string LastDeltaSignature { get; set; } = string.Empty;
 }
 
 public sealed class ShipRuntime
@@ -53,6 +56,7 @@ public sealed class ShipRuntime
   public required string FactionId { get; init; }
   public required Vector3 Position { get; set; }
   public required Vector3 TargetPosition { get; set; }
+  public Vector3 Velocity { get; set; } = Vector3.Zero;
   public string State { get; set; } = "idle";
   public ShipOrderRuntime? Order { get; set; }
   public required DefaultBehaviorRuntime DefaultBehavior { get; set; }
@@ -63,6 +67,7 @@ public sealed class ShipRuntime
   public float Health { get; set; }
   public List<string> History { get; } = [];
   public string LastSignature { get; set; } = string.Empty;
+  public string LastDeltaSignature { get; set; } = string.Empty;
 }
 
 public sealed class FactionRuntime
@@ -75,6 +80,7 @@ public sealed class FactionRuntime
   public float GoodsProduced { get; set; }
   public int ShipsBuilt { get; set; }
   public int ShipsLost { get; set; }
+  public string LastDeltaSignature { get; set; } = string.Empty;
 }
 
 public sealed class ShipOrderRuntime
@@ -131,4 +137,16 @@ public readonly record struct Vector3(float X, float Y, float Z)
       Y + ((target.Y - Y) * t),
       Z + ((target.Z - Z) * t));
   }
+
+  public Vector3 Subtract(Vector3 other) => new(X - other.X, Y - other.Y, Z - other.Z);
+
+  public Vector3 Divide(float value)
+  {
+    if (value == 0f)
+    {
+      return Zero;
+    }
+
+    return new(X / value, Y / value, Z / value);
+  }
 }
diff --git a/apps/backend/Simulation/SimulationEngine.cs b/apps/backend/Simulation/SimulationEngine.cs
index 09d643a..67392c6 100644
--- a/apps/backend/Simulation/SimulationEngine.cs
+++ b/apps/backend/Simulation/SimulationEngine.cs
@@ -4,27 +4,52 @@ namespace SpaceGame.Simulation.Api.Simulation;
 
 public sealed class SimulationEngine
 {
-  public void Tick(SimulationWorld world, float deltaSeconds)
+  public WorldDelta Tick(SimulationWorld world, float deltaSeconds, long sequence)
   {
-    UpdateStations(world, deltaSeconds);
+    var events = new List<SimulationEventRecord>();
+
+    UpdateStations(world, deltaSeconds, events);
 
     foreach (var ship in world.Ships)
     {
+      var previousPosition = ship.Position;
+      var previousState = ship.State;
+      var previousBehavior = ship.DefaultBehavior.Kind;
+      var previousTask = ship.ControllerTask.Kind;
+
       RefreshControlLayers(ship);
       PlanControllerTask(ship, world);
       var controllerEvent = UpdateControllerTask(ship, world, deltaSeconds);
       AdvanceControlState(ship, controllerEvent);
+      ship.Velocity = ship.Position.Subtract(previousPosition).Divide(deltaSeconds);
       TrackHistory(ship);
+
+      EmitShipStateEvents(ship, previousState, previousBehavior, previousTask, controllerEvent, events);
     }
 
     world.GeneratedAtUtc = DateTimeOffset.UtcNow;
+
+    return new WorldDelta(
+      sequence,
+      world.TickIntervalMs,
+      world.GeneratedAtUtc,
+      false,
+      events,
+      BuildNodeDeltas(world),
+      BuildStationDeltas(world),
+      BuildShipDeltas(world),
+      BuildFactionDeltas(world));
   }
 
-  public WorldSnapshot BuildSnapshot(SimulationWorld world)
+  public WorldSnapshot BuildSnapshot(SimulationWorld world, long sequence)
   {
+    PrimeDeltaBaseline(world);
+
     return new WorldSnapshot(
       world.Label,
       world.Seed,
+      sequence,
+      world.TickIntervalMs,
       world.GeneratedAtUtc,
       world.Systems.Select((system) => new SystemSnapshot(
         system.Definition.Id,
@@ -38,42 +63,44 @@ public sealed class SimulationEngine
           planet.Size,
           planet.Color,
           planet.HasRing)).ToList())).ToList(),
-      world.Nodes.Select((node) => new ResourceNodeSnapshot(
+      world.Nodes.Select(ToNodeDelta).Select((node) => new ResourceNodeSnapshot(
         node.Id,
         node.SystemId,
-        ToDto(node.Position),
+        node.Position,
         node.OreRemaining,
         node.MaxOre,
         node.ItemId)).ToList(),
-      world.Stations.Select((station) => new StationSnapshot(
+      world.Stations.Select(ToStationDelta).Select((station) => new StationSnapshot(
         station.Id,
-        station.Definition.Label,
-        station.Definition.Category,
+        station.Label,
+        station.Category,
         station.SystemId,
-        ToDto(station.Position),
-        station.Definition.Color,
-        station.DockedShipIds.Count,
+        station.Position,
+        station.Color,
+        station.DockedShips,
         station.OreStored,
         station.RefinedStock,
         station.FactionId)).ToList(),
-      world.Ships.Select((ship) => new ShipSnapshot(
+      world.Ships.Select(ToShipDelta).Select((ship) => new ShipSnapshot(
         ship.Id,
-        ship.Definition.Label,
-        ship.Definition.Role,
-        ship.Definition.ShipClass,
+        ship.Label,
+        ship.Role,
+        ship.ShipClass,
         ship.SystemId,
-        ToDto(ship.Position),
+        ship.Position,
+        ship.Velocity,
+        ship.TargetPosition,
         ship.State,
-        ship.Order?.Kind,
-        ship.DefaultBehavior.Kind,
-        ship.ControllerTask.Kind,
+        ship.OrderKind,
+        ship.DefaultBehaviorKind,
+        ship.ControllerTaskKind,
         ship.Cargo,
-        ship.Definition.CargoCapacity,
-        ship.Definition.CargoItemId,
+        ship.CargoCapacity,
+        ship.CargoItemId,
         ship.FactionId,
         ship.Health,
-        ship.History.ToList())).ToList(),
-      world.Factions.Select((faction) => new FactionSnapshot(
+        ship.History)).ToList(),
+      world.Factions.Select(ToFactionDelta).Select((faction) => new FactionSnapshot(
         faction.Id,
         faction.Label,
         faction.Color,
@@ -84,7 +111,211 @@ public sealed class SimulationEngine
         faction.ShipsLost)).ToList());
   }
 
-  private void UpdateStations(SimulationWorld world, float deltaSeconds)
+  public void PrimeDeltaBaseline(SimulationWorld world)
+  {
+    foreach (var node in world.Nodes)
+    {
+      node.LastDeltaSignature = BuildNodeSignature(node);
+    }
+
+    foreach (var station in world.Stations)
+    {
+      station.LastDeltaSignature = BuildStationSignature(station);
+    }
+
+    foreach (var ship in world.Ships)
+    {
+      ship.LastDeltaSignature = BuildShipSignature(ship);
+    }
+
+    foreach (var faction in world.Factions)
+    {
+      faction.LastDeltaSignature = BuildFactionSignature(faction);
+    }
+  }
+
+  private static IReadOnlyList<ResourceNodeDelta> BuildNodeDeltas(SimulationWorld world)
+  {
+    var deltas = new List<ResourceNodeDelta>();
+    foreach (var node in world.Nodes)
+    {
+      var signature = BuildNodeSignature(node);
+      if (signature == node.LastDeltaSignature)
+      {
+        continue;
+      }
+
+      node.LastDeltaSignature = signature;
+      deltas.Add(ToNodeDelta(node));
+    }
+
+    return deltas;
+  }
+
+  private static IReadOnlyList<StationDelta> BuildStationDeltas(SimulationWorld world)
+  {
+    var deltas = new List<StationDelta>();
+    foreach (var station in world.Stations)
+    {
+      var signature = BuildStationSignature(station);
+      if (signature == station.LastDeltaSignature)
+      {
+        continue;
+      }
+
+      station.LastDeltaSignature = signature;
+      deltas.Add(ToStationDelta(station));
+    }
+
+    return deltas;
+  }
+
+  private static IReadOnlyList<ShipDelta> BuildShipDeltas(SimulationWorld world)
+  {
+    var deltas = new List<ShipDelta>();
+    foreach (var ship in world.Ships)
+    {
+      var signature = BuildShipSignature(ship);
+      if (signature == ship.LastDeltaSignature)
+      {
+        continue;
+      }
+
+      ship.LastDeltaSignature = signature;
+      deltas.Add(ToShipDelta(ship));
+    }
+
+    return deltas;
+  }
+
+  private static IReadOnlyList<FactionDelta> BuildFactionDeltas(SimulationWorld world)
+  {
+    var deltas = new List<FactionDelta>();
+    foreach (var faction in world.Factions)
+    {
+      var signature = BuildFactionSignature(faction);
+      if (signature == faction.LastDeltaSignature)
+      {
+        continue;
+      }
+
+      faction.LastDeltaSignature = signature;
+      deltas.Add(ToFactionDelta(faction));
+    }
+
+    return deltas;
+  }
+
+  private static string BuildNodeSignature(ResourceNodeRuntime node) =>
+    $"{node.SystemId}|{node.OreRemaining:0.###}";
+
+  private static string BuildStationSignature(StationRuntime station) =>
+    $"{station.SystemId}|{station.OreStored:0.###}|{station.RefinedStock:0.###}|{station.DockedShipIds.Count}";
+
+  private static string BuildShipSignature(ShipRuntime ship) =>
+    string.Join("|",
+      ship.SystemId,
+      ship.Position.X.ToString("0.###"),
+      ship.Position.Y.ToString("0.###"),
+      ship.Position.Z.ToString("0.###"),
+      ship.Velocity.X.ToString("0.###"),
+      ship.Velocity.Y.ToString("0.###"),
+      ship.Velocity.Z.ToString("0.###"),
+      ship.TargetPosition.X.ToString("0.###"),
+      ship.TargetPosition.Y.ToString("0.###"),
+      ship.TargetPosition.Z.ToString("0.###"),
+      ship.State,
+      ship.Order?.Kind ?? "none",
+      ship.DefaultBehavior.Kind,
+      ship.ControllerTask.Kind,
+      ship.Cargo.ToString("0.###"),
+      ship.Health.ToString("0.###"));
+
+  private static string BuildFactionSignature(FactionRuntime faction) =>
+    $"{faction.Credits:0.###}|{faction.OreMined:0.###}|{faction.GoodsProduced:0.###}|{faction.ShipsBuilt}|{faction.ShipsLost}";
+
+  private static ResourceNodeDelta ToNodeDelta(ResourceNodeRuntime node) => new(
+    node.Id,
+    node.SystemId,
+    ToDto(node.Position),
+    node.OreRemaining,
+    node.MaxOre,
+    node.ItemId);
+
+  private static StationDelta ToStationDelta(StationRuntime station) => new(
+    station.Id,
+    station.Definition.Label,
+    station.Definition.Category,
+    station.SystemId,
+    ToDto(station.Position),
+    station.Definition.Color,
+    station.DockedShipIds.Count,
+    station.OreStored,
+    station.RefinedStock,
+    station.FactionId);
+
+  private static ShipDelta ToShipDelta(ShipRuntime ship) => new(
+    ship.Id,
+    ship.Definition.Label,
+    ship.Definition.Role,
+    ship.Definition.ShipClass,
+    ship.SystemId,
+    ToDto(ship.Position),
+    ToDto(ship.Velocity),
+    ToDto(ship.TargetPosition),
+    ship.State,
+    ship.Order?.Kind,
+    ship.DefaultBehavior.Kind,
+    ship.ControllerTask.Kind,
+    ship.Cargo,
+    ship.Definition.CargoCapacity,
+    ship.Definition.CargoItemId,
+    ship.FactionId,
+    ship.Health,
+    ship.History.ToList());
+
+  private static FactionDelta ToFactionDelta(FactionRuntime faction) => new(
+    faction.Id,
+    faction.Label,
+    faction.Color,
+    faction.Credits,
+    faction.OreMined,
+    faction.GoodsProduced,
+    faction.ShipsBuilt,
+    faction.ShipsLost);
+
+  private static void EmitShipStateEvents(
+    ShipRuntime ship,
+    string previousState,
+    string previousBehavior,
+    string previousTask,
+    string controllerEvent,
+    ICollection<SimulationEventRecord> events)
+  {
+    var occurredAtUtc = DateTimeOffset.UtcNow;
+
+    if (previousState != ship.State)
+    {
+      events.Add(new SimulationEventRecord("ship", ship.Id, "state-changed", $"{ship.Definition.Label} {previousState} -> {ship.State}", occurredAtUtc));
+    }
+
+    if (previousBehavior != ship.DefaultBehavior.Kind)
+    {
+      events.Add(new SimulationEventRecord("ship", ship.Id, "behavior-changed", $"{ship.Definition.Label} behavior {previousBehavior} -> {ship.DefaultBehavior.Kind}", occurredAtUtc));
+    }
+
+    if (previousTask != ship.ControllerTask.Kind)
+    {
+      events.Add(new SimulationEventRecord("ship", ship.Id, "task-changed", $"{ship.Definition.Label} task {previousTask} -> {ship.ControllerTask.Kind}", occurredAtUtc));
+    }
+
+    if (controllerEvent != "none")
+    {
+      events.Add(new SimulationEventRecord("ship", ship.Id, controllerEvent, $"{ship.Definition.Label} {controllerEvent}", occurredAtUtc));
+    }
+  }
+
+  private void UpdateStations(SimulationWorld world, float deltaSeconds, ICollection<SimulationEventRecord> events)
   {
     foreach (var station in world.Stations)
     {
@@ -102,6 +333,7 @@ public sealed class SimulationEngine
       station.ProcessTimer = 0f;
       station.OreStored -= 60f;
       station.RefinedStock += 60f;
+      events.Add(new SimulationEventRecord("station", station.Id, "refined", $"{station.Definition.Label} refined 60 ore", DateTimeOffset.UtcNow));
       var faction = world.Factions.FirstOrDefault((candidate) => candidate.Id == station.FactionId);
       if (faction is not null)
       {
@@ -251,6 +483,7 @@ public sealed class SimulationEngine
     {
       case "idle":
         ship.State = "idle";
+        ship.TargetPosition = ship.Position;
         return "none";
       case "travel":
         return UpdateTravel(ship, world, deltaSeconds);
@@ -264,6 +497,7 @@ public sealed class SimulationEngine
         return UpdateUndock(ship, world, deltaSeconds);
       default:
         ship.State = "idle";
+        ship.TargetPosition = ship.Position;
         return "none";
     }
   }
@@ -274,9 +508,11 @@ public sealed class SimulationEngine
     if (task.TargetPosition is null || task.TargetSystemId is null)
     {
       ship.State = "idle";
+      ship.TargetPosition = ship.Position;
       return "none";
     }
 
+    ship.TargetPosition = task.TargetPosition.Value;
     var distance = ship.Position.DistanceTo(task.TargetPosition.Value);
     if (distance <= task.Threshold)
     {
@@ -305,7 +541,6 @@ public sealed class SimulationEngine
     }
 
     ship.Position = ship.Position.MoveToward(task.TargetPosition.Value, speed * deltaSeconds);
-    ship.TargetPosition = task.TargetPosition.Value;
     return "none";
   }
 
@@ -316,9 +551,11 @@ public sealed class SimulationEngine
     if (node is null || task.TargetPosition is null)
     {
       ship.State = "idle";
+      ship.TargetPosition = ship.Position;
       return "none";
     }
 
+    ship.TargetPosition = task.TargetPosition.Value;
     var distance = ship.Position.DistanceTo(task.TargetPosition.Value);
     if (distance > task.Threshold)
     {
@@ -354,9 +591,11 @@ public sealed class SimulationEngine
     if (station is null || task.TargetPosition is null)
     {
       ship.State = "idle";
+      ship.TargetPosition = ship.Position;
       return "none";
     }
 
+    ship.TargetPosition = task.TargetPosition.Value;
     var distance = ship.Position.DistanceTo(task.TargetPosition.Value);
     if (distance > task.Threshold)
     {
@@ -377,6 +616,7 @@ public sealed class SimulationEngine
     ship.DockedStationId = station.Id;
     station.DockedShipIds.Add(ship.Id);
     ship.Position = station.Position;
+    ship.TargetPosition = station.Position;
     return "docked";
   }
 
@@ -385,6 +625,7 @@ public sealed class SimulationEngine
     if (ship.DockedStationId is null)
     {
       ship.State = "idle";
+      ship.TargetPosition = ship.Position;
       return "none";
     }
 
@@ -393,9 +634,11 @@ public sealed class SimulationEngine
     {
       ship.DockedStationId = null;
       ship.State = "idle";
+      ship.TargetPosition = ship.Position;
       return "none";
     }
 
+    ship.TargetPosition = station.Position;
     ship.State = "transferring";
     var moved = MathF.Min(ship.Cargo, world.Balance.TransferRate * deltaSeconds);
     ship.Cargo -= moved;
@@ -416,9 +659,11 @@ public sealed class SimulationEngine
     if (ship.DockedStationId is null || task.TargetPosition is null)
     {
       ship.State = "idle";
+      ship.TargetPosition = ship.Position;
       return "none";
     }
 
+    ship.TargetPosition = task.TargetPosition.Value;
     var station = world.Stations.FirstOrDefault((candidate) => candidate.Id == ship.DockedStationId);
     station?.DockedShipIds.Remove(ship.Id);
     ship.DockedStationId = null;
diff --git a/apps/backend/Simulation/WorldService.cs b/apps/backend/Simulation/WorldService.cs
index f43d2bb..6e34e5a 100644
--- a/apps/backend/Simulation/WorldService.cs
+++ b/apps/backend/Simulation/WorldService.cs
@@ -1,27 +1,81 @@
+using System.Threading.Channels;
 using SpaceGame.Simulation.Api.Contracts;
 
 namespace SpaceGame.Simulation.Api.Simulation;
 
 public sealed class WorldService(IWebHostEnvironment environment)
 {
+  private const int DeltaHistoryLimit = 256;
+
   private readonly object _sync = new();
   private readonly ScenarioLoader _loader = new(environment.ContentRootPath);
   private readonly SimulationEngine _engine = new();
+  private readonly Dictionary<Guid, Channel<WorldDelta>> _subscribers = [];
+  private readonly Queue<WorldDelta> _history = [];
   private SimulationWorld _world = new ScenarioLoader(environment.ContentRootPath).Load();
+  private long _sequence;
 
   public WorldSnapshot GetSnapshot()
   {
     lock (_sync)
     {
-      return _engine.BuildSnapshot(_world);
+      return _engine.BuildSnapshot(_world, _sequence);
     }
   }
 
+  public (long Sequence, DateTimeOffset GeneratedAtUtc) GetStatus()
+  {
+    lock (_sync)
+    {
+      return (_sequence, _world.GeneratedAtUtc);
+    }
+  }
+
+  public ChannelReader<WorldDelta> Subscribe(long afterSequence, CancellationToken cancellationToken)
+  {
+    var channel = Channel.CreateUnbounded<WorldDelta>(new UnboundedChannelOptions
+    {
+      SingleReader = true,
+      SingleWriter = false,
+    });
+
+    Guid subscriberId;
+    lock (_sync)
+    {
+      subscriberId = Guid.NewGuid();
+      _subscribers.Add(subscriberId, channel);
+
+      foreach (var delta in _history.Where((candidate) => candidate.Sequence > afterSequence))
+      {
+        channel.Writer.TryWrite(delta);
+      }
+    }
+
+    cancellationToken.Register(() => Unsubscribe(subscriberId));
+    return channel.Reader;
+  }
+
   public void Tick(float deltaSeconds)
   {
+    WorldDelta? delta = null;
     lock (_sync)
     {
-      _engine.Tick(_world, deltaSeconds);
+      delta = _engine.Tick(_world, deltaSeconds, ++_sequence);
+      if (!HasMeaningfulDelta(delta))
+      {
+        return;
+      }
+
+      _history.Enqueue(delta);
+      while (_history.Count > DeltaHistoryLimit)
+      {
+        _history.Dequeue();
+      }
+
+      foreach (var subscriber in _subscribers.Values.ToList())
+      {
+        subscriber.Writer.TryWrite(delta);
+      }
     }
   }
 
@@ -30,7 +84,48 @@ public sealed class WorldService(IWebHostEnvironment environment)
     lock (_sync)
     {
       _world = _loader.Load();
-      return _engine.BuildSnapshot(_world);
+      _sequence += 1;
+      _history.Clear();
+
+      var resetDelta = new WorldDelta(
+        _sequence,
+        _world.TickIntervalMs,
+        DateTimeOffset.UtcNow,
+        true,
+        [new SimulationEventRecord("world", "world", "reset", "World reset requested", DateTimeOffset.UtcNow)],
+        [],
+        [],
+        [],
+        []);
+
+      _history.Enqueue(resetDelta);
+      foreach (var subscriber in _subscribers.Values.ToList())
+      {
+        subscriber.Writer.TryWrite(resetDelta);
+      }
+
+      return _engine.BuildSnapshot(_world, _sequence);
+    }
+  }
+
+  private static bool HasMeaningfulDelta(WorldDelta delta) =>
+    delta.RequiresSnapshotRefresh
+    || delta.Events.Count > 0
+    || delta.Nodes.Count > 0
+    || delta.Stations.Count > 0
+    || delta.Ships.Count > 0
+    || delta.Factions.Count > 0;
+
+  private void Unsubscribe(Guid subscriberId)
+  {
+    lock (_sync)
+    {
+      if (!_subscribers.Remove(subscriberId, out var channel))
+      {
+        return;
+      }
+
+      channel.Writer.TryComplete();
     }
   }
 }
diff --git a/apps/viewer/src/GameViewer.ts b/apps/viewer/src/GameViewer.ts
index 3337e9f..e3266e0 100644
--- a/apps/viewer/src/GameViewer.ts
+++ b/apps/viewer/src/GameViewer.ts
@@ -1,11 +1,18 @@
 import * as THREE from "three";
-import { fetchWorldSnapshot, resetWorld } from "./api";
+import { fetchWorldSnapshot, openWorldStream, resetWorld } from "./api";
 import type {
+  FactionDelta,
   FactionSnapshot,
+  ResourceNodeDelta,
   ResourceNodeSnapshot,
+  ShipDelta,
   ShipSnapshot,
+  SimulationEventRecord,
+  StationDelta,
   StationSnapshot,
   SystemSnapshot,
+  Vector3Dto,
+  WorldDelta,
   WorldSnapshot,
 } from "./contracts";
 
@@ -15,6 +22,30 @@ type Selectable =
   | { kind: "node"; id: string }
   | { kind: "system"; id: string };
 
+interface ShipVisual {
+  mesh: THREE.Mesh;
+  startPosition: THREE.Vector3;
+  authoritativePosition: THREE.Vector3;
+  targetPosition: THREE.Vector3;
+  velocity: THREE.Vector3;
+  receivedAtMs: number;
+  blendDurationMs: number;
+}
+
+interface WorldState {
+  label: string;
+  seed: number;
+  sequence: number;
+  tickIntervalMs: number;
+  generatedAtUtc: string;
+  systems: Map<string, SystemSnapshot>;
+  nodes: Map<string, ResourceNodeSnapshot>;
+  stations: Map<string, StationSnapshot>;
+  ships: Map<string, ShipSnapshot>;
+  factions: Map<string, FactionSnapshot>;
+  recentEvents: SimulationEventRecord[];
+}
+
 export class GameViewer {
   private readonly container: HTMLElement;
   private readonly renderer = new THREE.WebGLRenderer({ antialias: true });
@@ -29,13 +60,18 @@ export class GameViewer {
   private readonly stationGroup = new THREE.Group();
   private readonly shipGroup = new THREE.Group();
   private readonly selectableTargets = new Map<THREE.Object3D, Selectable>();
+  private readonly nodeMeshes = new Map<string, THREE.Mesh>();
+  private readonly stationMeshes = new Map<string, THREE.Mesh>();
+  private readonly shipVisuals = new Map<string, ShipVisual>();
   private readonly statusEl: HTMLDivElement;
   private readonly detailTitleEl: HTMLHeadingElement;
   private readonly detailBodyEl: HTMLDivElement;
   private readonly factionStripEl: HTMLDivElement;
   private readonly resetButton: HTMLButtonElement;
   private readonly errorEl: HTMLDivElement;
-  private snapshot?: WorldSnapshot;
+  private readonly streamEl: HTMLDivElement;
+  private world?: WorldState;
+  private stream?: EventSource;
   private selected?: Selectable;
   private dragging = false;
   private lastPointer = new THREE.Vector2();
@@ -66,20 +102,22 @@ export class GameViewer {
           <h1>Space Game Observer</h1>
         </div>
         <div class="topbar-actions">
-          <div class="status-pill">Connecting</div>
+          <div class="status-pill">Bootstrapping</div>
+          <div class="status-pill stream-pill">Stream Offline</div>
           <button type="button" class="reset-button">Reset World</button>
         </div>
       </header>
       <aside class="details-panel">
         <h2>Selection</h2>
         <h3 class="detail-title">Nothing selected</h3>
-        <div class="detail-body">Click a star, station, node, or ship to inspect the server snapshot.</div>
+        <div class="detail-body">Waiting for the authoritative snapshot.</div>
         <div class="error-strip" hidden></div>
       </aside>
       <section class="faction-strip"></section>
     `;
 
     this.statusEl = hud.querySelector(".status-pill") as HTMLDivElement;
+    this.streamEl = hud.querySelector(".stream-pill") as HTMLDivElement;
     this.detailTitleEl = hud.querySelector(".detail-title") as HTMLHeadingElement;
     this.detailBodyEl = hud.querySelector(".detail-body") as HTMLDivElement;
     this.factionStripEl = hud.querySelector(".faction-strip") as HTMLDivElement;
@@ -100,55 +138,137 @@ export class GameViewer {
   }
 
   async start() {
-    await this.refreshSnapshot();
-    window.setInterval(() => {
-      void this.refreshSnapshot();
-    }, 500);
+    await this.bootstrapWorld();
     this.renderer.setAnimationLoop(() => this.render());
   }
 
-  private async refreshSnapshot() {
+  private async bootstrapWorld() {
     try {
       const snapshot = await fetchWorldSnapshot();
-      this.snapshot = snapshot;
-      this.statusEl.textContent = `Live ${new Date(snapshot.generatedAtUtc).toLocaleTimeString()}`;
+      this.world = this.createWorldState(snapshot);
+      this.statusEl.textContent = `Snapshot ${snapshot.sequence}`;
       this.errorEl.hidden = true;
       this.applySnapshot(snapshot);
+      this.openDeltaStream(snapshot.sequence);
       this.updatePanels();
     } catch (error) {
       this.statusEl.textContent = "Backend offline";
+      this.streamEl.textContent = "Stream Offline";
       this.errorEl.hidden = false;
-      this.errorEl.textContent = error instanceof Error ? error.message : "Unable to load the backend snapshot.";
+      this.errorEl.textContent = error instanceof Error ? error.message : "Unable to bootstrap the backend snapshot.";
     }
   }
 
+  private openDeltaStream(afterSequence: number) {
+    this.stream?.close();
+    this.stream = openWorldStream(afterSequence, {
+      onOpen: () => {
+        this.streamEl.textContent = "Stream Live";
+      },
+      onError: () => {
+        this.streamEl.textContent = "Stream Reconnecting";
+      },
+      onDelta: (delta) => {
+        void this.handleDelta(delta);
+      },
+    });
+  }
+
+  private async handleDelta(delta: WorldDelta) {
+    if (!this.world) {
+      return;
+    }
+
+    if (delta.requiresSnapshotRefresh) {
+      await this.bootstrapWorld();
+      return;
+    }
+
+    this.applyDelta(delta);
+    this.statusEl.textContent = `Seq ${delta.sequence} · ${new Date(delta.generatedAtUtc).toLocaleTimeString()}`;
+    this.updatePanels();
+  }
+
   private async handleReset() {
     this.resetButton.disabled = true;
     try {
       const snapshot = await resetWorld();
-      this.snapshot = snapshot;
+      this.world = this.createWorldState(snapshot);
       this.applySnapshot(snapshot);
+      this.openDeltaStream(snapshot.sequence);
       this.updatePanels();
     } finally {
       this.resetButton.disabled = false;
     }
   }
 
+  private createWorldState(snapshot: WorldSnapshot): WorldState {
+    return {
+      label: snapshot.label,
+      seed: snapshot.seed,
+      sequence: snapshot.sequence,
+      tickIntervalMs: snapshot.tickIntervalMs,
+      generatedAtUtc: snapshot.generatedAtUtc,
+      systems: new Map(snapshot.systems.map((system) => [system.id, system])),
+      nodes: new Map(snapshot.nodes.map((node) => [node.id, node])),
+      stations: new Map(snapshot.stations.map((station) => [station.id, station])),
+      ships: new Map(snapshot.ships.map((ship) => [ship.id, ship])),
+      factions: new Map(snapshot.factions.map((faction) => [faction.id, faction])),
+      recentEvents: [],
+    };
+  }
+
   private applySnapshot(snapshot: WorldSnapshot) {
     const signature = `${snapshot.seed}|${snapshot.systems.length}`;
     if (signature !== this.worldSignature) {
       this.worldSignature = signature;
       this.rebuildSystems(snapshot.systems);
     }
-    this.rebuildNodes(snapshot.nodes);
-    this.rebuildStations(snapshot.stations);
-    this.rebuildShips(snapshot.ships);
+
+    this.syncNodes(snapshot.nodes);
+    this.syncStations(snapshot.stations);
+    this.syncShips(snapshot.ships, snapshot.tickIntervalMs);
     this.rebuildFactions(snapshot.factions);
   }
 
+  private applyDelta(delta: WorldDelta) {
+    if (!this.world) {
+      return;
+    }
+
+    this.world.sequence = delta.sequence;
+    this.world.tickIntervalMs = delta.tickIntervalMs;
+    this.world.generatedAtUtc = delta.generatedAtUtc;
+    this.world.recentEvents = [...delta.events, ...this.world.recentEvents].slice(0, 18);
+
+    for (const node of delta.nodes) {
+      this.world.nodes.set(node.id, node);
+    }
+
+    for (const station of delta.stations) {
+      this.world.stations.set(station.id, station);
+    }
+
+    for (const ship of delta.ships) {
+      this.world.ships.set(ship.id, ship);
+    }
+
+    for (const faction of delta.factions) {
+      this.world.factions.set(faction.id, faction);
+    }
+
+    this.applyNodeDeltas(delta.nodes);
+    this.applyStationDeltas(delta.stations);
+    this.applyShipDeltas(delta.ships, delta.tickIntervalMs);
+    if (delta.factions.length > 0) {
+      this.rebuildFactions([...this.world.factions.values()]);
+    }
+  }
+
   private rebuildSystems(systems: SystemSnapshot[]) {
     this.systemGroup.clear();
     this.selectableTargets.clear();
+
     for (const system of systems) {
       const root = new THREE.Group();
       root.position.set(system.position.x, system.position.y, system.position.z);
@@ -168,6 +288,7 @@ export class GameViewer {
       root.add(star, halo);
       this.selectableTargets.set(star, { kind: "system", id: system.id });
       this.selectableTargets.set(halo, { kind: "system", id: system.id });
+
       for (const planet of system.planets) {
         const orbit = new THREE.LineLoop(
           new THREE.BufferGeometry().setFromPoints(
@@ -193,50 +314,115 @@ export class GameViewer {
         planetMesh.position.set(planet.orbitRadius, 0, 0);
         root.add(orbit, planetMesh);
       }
+
       this.systemGroup.add(root);
     }
   }
 
-  private rebuildNodes(nodes: ResourceNodeSnapshot[]) {
+  private syncNodes(nodes: ResourceNodeSnapshot[]) {
     this.nodeGroup.clear();
+    this.nodeMeshes.clear();
     for (const node of nodes) {
-      const mesh = new THREE.Mesh(
-        new THREE.IcosahedronGeometry(12, 0),
-        new THREE.MeshStandardMaterial({ color: 0xd2b07a, flatShading: true }),
-      );
-      mesh.position.set(node.position.x, node.position.y, node.position.z);
-      mesh.scale.setScalar(0.8 + (node.oreRemaining / Math.max(node.maxOre, 1)) * 0.6);
+      const mesh = this.createNodeMesh(node);
+      this.nodeMeshes.set(node.id, mesh);
       this.nodeGroup.add(mesh);
       this.selectableTargets.set(mesh, { kind: "node", id: node.id });
     }
   }
 
-  private rebuildStations(stations: StationSnapshot[]) {
+  private syncStations(stations: StationSnapshot[]) {
     this.stationGroup.clear();
+    this.stationMeshes.clear();
     for (const station of stations) {
-      const mesh = new THREE.Mesh(
-        new THREE.CylinderGeometry(24, 24, 18, 10),
-        new THREE.MeshStandardMaterial({ color: station.color, emissive: new THREE.Color(station.color).multiplyScalar(0.1) }),
-      );
-      mesh.rotation.x = Math.PI / 2;
-      mesh.position.set(station.position.x, station.position.y, station.position.z);
+      const mesh = this.createStationMesh(station);
+      this.stationMeshes.set(station.id, mesh);
       this.stationGroup.add(mesh);
       this.selectableTargets.set(mesh, { kind: "station", id: station.id });
     }
   }
 
-  private rebuildShips(ships: ShipSnapshot[]) {
+  private syncShips(ships: ShipSnapshot[], tickIntervalMs: number) {
     this.shipGroup.clear();
+    this.shipVisuals.clear();
     for (const ship of ships) {
-      const geometry = new THREE.ConeGeometry(this.shipSize(ship), this.shipLength(ship), 7);
-      geometry.rotateX(Math.PI / 2);
-      const mesh = new THREE.Mesh(
-        geometry,
-        new THREE.MeshStandardMaterial({ color: this.shipColor(ship.role) }),
-      );
-      mesh.position.set(ship.position.x, ship.position.y, ship.position.z);
+      const mesh = this.createShipMesh(ship);
       this.shipGroup.add(mesh);
       this.selectableTargets.set(mesh, { kind: "ship", id: ship.id });
+      const position = this.toThreeVector(ship.position);
+      this.shipVisuals.set(ship.id, {
+        mesh,
+        startPosition: position.clone(),
+        authoritativePosition: position.clone(),
+        targetPosition: this.toThreeVector(ship.targetPosition),
+        velocity: this.toThreeVector(ship.velocity),
+        receivedAtMs: performance.now(),
+        blendDurationMs: Math.max(tickIntervalMs, 80),
+      });
+    }
+  }
+
+  private applyNodeDeltas(nodes: ResourceNodeDelta[]) {
+    for (const node of nodes) {
+      const mesh = this.nodeMeshes.get(node.id);
+      if (!mesh) {
+        const nextMesh = this.createNodeMesh(node);
+        this.nodeMeshes.set(node.id, nextMesh);
+        this.nodeGroup.add(nextMesh);
+        this.selectableTargets.set(nextMesh, { kind: "node", id: node.id });
+        continue;
+      }
+
+      mesh.position.copy(this.toThreeVector(node.position));
+      mesh.scale.setScalar(0.8 + (node.oreRemaining / Math.max(node.maxOre, 1)) * 0.6);
+    }
+  }
+
+  private applyStationDeltas(stations: StationDelta[]) {
+    for (const station of stations) {
+      const mesh = this.stationMeshes.get(station.id);
+      if (!mesh) {
+        const nextMesh = this.createStationMesh(station);
+        this.stationMeshes.set(station.id, nextMesh);
+        this.stationGroup.add(nextMesh);
+        this.selectableTargets.set(nextMesh, { kind: "station", id: station.id });
+        continue;
+      }
+
+      mesh.position.copy(this.toThreeVector(station.position));
+      const material = mesh.material as THREE.MeshStandardMaterial;
+      material.color.set(station.color);
+      material.emissive = new THREE.Color(station.color).multiplyScalar(0.1);
+    }
+  }
+
+  private applyShipDeltas(ships: ShipDelta[], tickIntervalMs: number) {
+    for (const ship of ships) {
+      const visual = this.shipVisuals.get(ship.id);
+      if (!visual) {
+        const mesh = this.createShipMesh(ship);
+        const position = this.toThreeVector(ship.position);
+        this.shipGroup.add(mesh);
+        this.selectableTargets.set(mesh, { kind: "ship", id: ship.id });
+        this.shipVisuals.set(ship.id, {
+          mesh,
+          startPosition: position.clone(),
+          authoritativePosition: position.clone(),
+          targetPosition: this.toThreeVector(ship.targetPosition),
+          velocity: this.toThreeVector(ship.velocity),
+          receivedAtMs: performance.now(),
+          blendDurationMs: Math.max(tickIntervalMs, 80),
+        });
+        continue;
+      }
+
+      visual.startPosition.copy(visual.mesh.position);
+      visual.authoritativePosition.copy(this.toThreeVector(ship.position));
+      visual.targetPosition.copy(this.toThreeVector(ship.targetPosition));
+      visual.velocity.copy(this.toThreeVector(ship.velocity));
+      visual.receivedAtMs = performance.now();
+      visual.blendDurationMs = Math.max(tickIntervalMs * 1.35, 100);
+      const material = visual.mesh.material as THREE.MeshStandardMaterial;
+      material.color.set(this.shipColor(ship.role));
     }
   }
 
@@ -255,71 +441,153 @@ export class GameViewer {
   }
 
   private updatePanels() {
-    if (!this.snapshot) {
+    if (!this.world) {
       return;
     }
+
     if (!this.selected) {
-      this.detailTitleEl.textContent = this.snapshot.label;
-      this.detailBodyEl.innerHTML = `Systems ${this.snapshot.systems.length}<br>Stations ${this.snapshot.stations.length}<br>Ships ${this.snapshot.ships.length}`;
-      return;
-    }
-
-    const selected = this.selected;
-    if (selected.kind === "ship") {
-      const ship = this.snapshot.ships.find((candidate) => candidate.id === selected.id);
-      if (ship) {
-        this.detailTitleEl.textContent = ship.label;
-        this.detailBodyEl.innerHTML = `
-          <p>${ship.shipClass} · ${ship.role} · ${ship.systemId}</p>
-          <p>State ${ship.state}<br>Behavior ${ship.defaultBehaviorKind}<br>Task ${ship.controllerTaskKind}</p>
-          <p>Cargo ${ship.cargo.toFixed(0)} / ${ship.cargoCapacity.toFixed(0)} ${ship.cargoItemId ?? ""}</p>
-          <p class="history">${ship.history.join("<br>")}</p>
-        `;
-      }
-      return;
-    }
-
-    if (selected.kind === "station") {
-      const station = this.snapshot.stations.find((candidate) => candidate.id === selected.id);
-      if (station) {
-        this.detailTitleEl.textContent = station.label;
-        this.detailBodyEl.innerHTML = `
-          <p>${station.category} · ${station.systemId}</p>
-          <p>Ore ${station.oreStored.toFixed(0)}<br>Refined ${station.refinedStock.toFixed(0)}<br>Docked ${station.dockedShips}</p>
-        `;
-      }
-      return;
-    }
-
-    if (selected.kind === "node") {
-      const node = this.snapshot.nodes.find((candidate) => candidate.id === selected.id);
-      if (node) {
-        this.detailTitleEl.textContent = `Node ${node.id}`;
-        this.detailBodyEl.innerHTML = `
-          <p>${node.systemId}</p>
-          <p>${node.itemId} ${node.oreRemaining.toFixed(0)} / ${node.maxOre.toFixed(0)}</p>
-        `;
-      }
-      return;
-    }
-
-    const system = this.snapshot.systems.find((candidate) => candidate.id === selected.id);
-    if (system) {
-      this.detailTitleEl.textContent = system.label;
+      this.detailTitleEl.textContent = this.world.label;
       this.detailBodyEl.innerHTML = `
-        <p>${system.id}</p>
-        <p>Planets ${system.planets.length}</p>
+        Systems ${this.world.systems.size}<br>
+        Stations ${this.world.stations.size}<br>
+        Ships ${this.world.ships.size}<br>
+        Recent events ${this.world.recentEvents.length}
       `;
+      return;
     }
+
+    if (this.selected.kind === "ship") {
+      const ship = this.world.ships.get(this.selected.id);
+      if (!ship) {
+        return;
+      }
+      this.detailTitleEl.textContent = ship.label;
+      this.detailBodyEl.innerHTML = `
+        <p>${ship.shipClass} · ${ship.role} · ${ship.systemId}</p>
+        <p>State ${ship.state}<br>Behavior ${ship.defaultBehaviorKind}<br>Task ${ship.controllerTaskKind}</p>
+        <p>Cargo ${ship.cargo.toFixed(0)} / ${ship.cargoCapacity.toFixed(0)} ${ship.cargoItemId ?? ""}</p>
+        <p>Velocity ${this.formatVector(ship.velocity)}</p>
+        <p class="history">${ship.history.join("<br>")}</p>
+      `;
+      return;
+    }
+
+    if (this.selected.kind === "station") {
+      const station = this.world.stations.get(this.selected.id);
+      if (!station) {
+        return;
+      }
+      this.detailTitleEl.textContent = station.label;
+      this.detailBodyEl.innerHTML = `
+        <p>${station.category} · ${station.systemId}</p>
+        <p>Ore ${station.oreStored.toFixed(0)}<br>Refined ${station.refinedStock.toFixed(0)}<br>Docked ${station.dockedShips}</p>
+        <p class="history">${this.renderRecentEvents("station", station.id)}</p>
+      `;
+      return;
+    }
+
+    if (this.selected.kind === "node") {
+      const node = this.world.nodes.get(this.selected.id);
+      if (!node) {
+        return;
+      }
+      this.detailTitleEl.textContent = `Node ${node.id}`;
+      this.detailBodyEl.innerHTML = `
+        <p>${node.systemId}</p>
+        <p>${node.itemId} ${node.oreRemaining.toFixed(0)} / ${node.maxOre.toFixed(0)}</p>
+      `;
+      return;
+    }
+
+    const system = this.world.systems.get(this.selected.id);
+    if (!system) {
+      return;
+    }
+    this.detailTitleEl.textContent = system.label;
+    this.detailBodyEl.innerHTML = `
+      <p>${system.id}</p>
+      <p>Planets ${system.planets.length}</p>
+    `;
   }
 
   private render() {
     const delta = Math.min(this.clock.getDelta(), 0.033);
     this.camera.position.lerp(new THREE.Vector3(this.focus.x + 2200, 1600, this.focus.z + 2200), Math.min(1, delta * 2));
     this.camera.lookAt(this.focus);
+    this.updateShipPresentation();
     this.renderer.render(this.scene, this.camera);
   }
 
+  private updateShipPresentation() {
+    const now = performance.now();
+    for (const visual of this.shipVisuals.values()) {
+      const elapsedMs = now - visual.receivedAtMs;
+      const blendT = THREE.MathUtils.clamp(elapsedMs / visual.blendDurationMs, 0, 1);
+      visual.mesh.position.lerpVectors(visual.startPosition, visual.authoritativePosition, blendT);
+
+      if (blendT >= 1) {
+        const extrapolationSeconds = Math.min((elapsedMs - visual.blendDurationMs) / 1000, 0.35);
+        visual.mesh.position.copy(visual.authoritativePosition).addScaledVector(visual.velocity, extrapolationSeconds);
+      }
+
+      const desiredHeading = visual.targetPosition.clone().sub(visual.mesh.position);
+      if (desiredHeading.lengthSq() > 0.01) {
+        visual.mesh.lookAt(visual.mesh.position.clone().add(desiredHeading));
+      }
+    }
+  }
+
+  private createNodeMesh(node: ResourceNodeSnapshot) {
+    const mesh = new THREE.Mesh(
+      new THREE.IcosahedronGeometry(12, 0),
+      new THREE.MeshStandardMaterial({ color: 0xd2b07a, flatShading: true }),
+    );
+    mesh.position.copy(this.toThreeVector(node.position));
+    mesh.scale.setScalar(0.8 + (node.oreRemaining / Math.max(node.maxOre, 1)) * 0.6);
+    return mesh;
+  }
+
+  private createStationMesh(station: StationSnapshot) {
+    const mesh = new THREE.Mesh(
+      new THREE.CylinderGeometry(24, 24, 18, 10),
+      new THREE.MeshStandardMaterial({ color: station.color, emissive: new THREE.Color(station.color).multiplyScalar(0.1) }),
+    );
+    mesh.rotation.x = Math.PI / 2;
+    mesh.position.copy(this.toThreeVector(station.position));
+    return mesh;
+  }
+
+  private createShipMesh(ship: ShipSnapshot) {
+    const geometry = new THREE.ConeGeometry(this.shipSize(ship), this.shipLength(ship), 7);
+    geometry.rotateX(Math.PI / 2);
+    const mesh = new THREE.Mesh(
+      geometry,
+      new THREE.MeshStandardMaterial({ color: this.shipColor(ship.role) }),
+    );
+    mesh.position.copy(this.toThreeVector(ship.position));
+    return mesh;
+  }
+
+  private renderRecentEvents(entityKind: string, entityId: string) {
+    if (!this.world) {
+      return "";
+    }
+
+    return this.world.recentEvents
+      .filter((event) => event.entityKind === entityKind && (!entityId || event.entityId === entityId))
+      .slice(0, 8)
+      .map((event) => `${new Date(event.occurredAtUtc).toLocaleTimeString()} ${event.message}`)
+      .join("<br>");
+  }
+
+  private formatVector(vector: Vector3Dto) {
+    return `${vector.x.toFixed(1)}, ${vector.y.toFixed(1)}, ${vector.z.toFixed(1)}`;
+  }
+
+  private toThreeVector(vector: Vector3Dto) {
+    return new THREE.Vector3(vector.x, vector.y, vector.z);
+  }
+
   private onPointerDown = (event: PointerEvent) => {
     this.dragging = true;
     this.lastPointer.set(event.clientX, event.clientY);
@@ -351,7 +619,7 @@ export class GameViewer {
   };
 
   private onDoubleClick = () => {
-    if (!this.snapshot || !this.selected) {
+    if (!this.world || !this.selected) {
       return;
     }
     const nextFocus = this.resolveSelectionPosition(this.selected);
@@ -369,23 +637,27 @@ export class GameViewer {
   };
 
   private resolveSelectionPosition(selection: Selectable) {
-    if (!this.snapshot) {
+    if (!this.world) {
       return undefined;
     }
+
     if (selection.kind === "ship") {
-      const ship = this.snapshot.ships.find((candidate) => candidate.id === selection.id);
-      return ship ? new THREE.Vector3(ship.position.x, ship.position.y, ship.position.z) : undefined;
+      const ship = this.world.ships.get(selection.id);
+      return ship ? this.toThreeVector(ship.position) : undefined;
     }
+
     if (selection.kind === "station") {
-      const station = this.snapshot.stations.find((candidate) => candidate.id === selection.id);
-      return station ? new THREE.Vector3(station.position.x, station.position.y, station.position.z) : undefined;
+      const station = this.world.stations.get(selection.id);
+      return station ? this.toThreeVector(station.position) : undefined;
     }
+
     if (selection.kind === "node") {
-      const node = this.snapshot.nodes.find((candidate) => candidate.id === selection.id);
-      return node ? new THREE.Vector3(node.position.x, node.position.y, node.position.z) : undefined;
+      const node = this.world.nodes.get(selection.id);
+      return node ? this.toThreeVector(node.position) : undefined;
     }
-    const system = this.snapshot.systems.find((candidate) => candidate.id === selection.id);
-    return system ? new THREE.Vector3(system.position.x, system.position.y, system.position.z) : undefined;
+
+    const system = this.world.systems.get(selection.id);
+    return system ? this.toThreeVector(system.position) : undefined;
   }
 
   private shipSize(ship: ShipSnapshot) {
diff --git a/apps/viewer/src/api.ts b/apps/viewer/src/api.ts
index c84c174..ce00052 100644
--- a/apps/viewer/src/api.ts
+++ b/apps/viewer/src/api.ts
@@ -1,4 +1,4 @@
-import type { WorldSnapshot } from "./contracts";
+import type { WorldDelta, WorldSnapshot } from "./contracts";
 
 export async function fetchWorldSnapshot(signal?: AbortSignal) {
   const response = await fetch("/api/world", { signal });
@@ -8,6 +8,24 @@ export async function fetchWorldSnapshot(signal?: AbortSignal) {
   return response.json() as Promise<WorldSnapshot>;
 }
 
+export function openWorldStream(
+  afterSequence: number,
+  handlers: {
+    onDelta: (delta: WorldDelta) => void;
+    onOpen?: () => void;
+    onError?: () => void;
+  },
+) {
+  const stream = new EventSource(`/api/world/stream?afterSequence=${afterSequence}`);
+  stream.addEventListener("open", () => handlers.onOpen?.());
+  stream.addEventListener("error", () => handlers.onError?.());
+  stream.addEventListener("world-delta", (event) => {
+    const message = event as MessageEvent<string>;
+    handlers.onDelta(JSON.parse(message.data) as WorldDelta);
+  });
+  return stream;
+}
+
 export async function resetWorld() {
   const response = await fetch("/api/world/reset", {
     method: "POST",
diff --git a/apps/viewer/src/contracts.ts b/apps/viewer/src/contracts.ts
index 4ec6b4f..5299642 100644
--- a/apps/viewer/src/contracts.ts
+++ b/apps/viewer/src/contracts.ts
@@ -1,6 +1,8 @@
 export interface WorldSnapshot {
   label: string;
   seed: number;
+  sequence: number;
+  tickIntervalMs: number;
   generatedAtUtc: string;
   systems: SystemSnapshot[];
   nodes: ResourceNodeSnapshot[];
@@ -9,6 +11,26 @@ export interface WorldSnapshot {
   factions: FactionSnapshot[];
 }
 
+export interface WorldDelta {
+  sequence: number;
+  tickIntervalMs: number;
+  generatedAtUtc: string;
+  requiresSnapshotRefresh: boolean;
+  events: SimulationEventRecord[];
+  nodes: ResourceNodeDelta[];
+  stations: StationDelta[];
+  ships: ShipDelta[];
+  factions: FactionDelta[];
+}
+
+export interface SimulationEventRecord {
+  entityKind: string;
+  entityId: string;
+  kind: string;
+  message: string;
+  occurredAtUtc: string;
+}
+
 export interface Vector3Dto {
   x: number;
   y: number;
@@ -41,6 +63,8 @@ export interface ResourceNodeSnapshot {
   itemId: string;
 }
 
+export interface ResourceNodeDelta extends ResourceNodeSnapshot {}
+
 export interface StationSnapshot {
   id: string;
   label: string;
@@ -54,6 +78,8 @@ export interface StationSnapshot {
   factionId: string;
 }
 
+export interface StationDelta extends StationSnapshot {}
+
 export interface ShipSnapshot {
   id: string;
   label: string;
@@ -61,6 +87,8 @@ export interface ShipSnapshot {
   shipClass: string;
   systemId: string;
   position: Vector3Dto;
+  velocity: Vector3Dto;
+  targetPosition: Vector3Dto;
   state: string;
   orderKind: string | null;
   defaultBehaviorKind: string;
@@ -73,6 +101,8 @@ export interface ShipSnapshot {
   history: string[];
 }
 
+export interface ShipDelta extends ShipSnapshot {}
+
 export interface FactionSnapshot {
   id: string;
   label: string;
@@ -83,3 +113,5 @@ export interface FactionSnapshot {
   shipsBuilt: number;
   shipsLost: number;
 }
+
+export interface FactionDelta extends FactionSnapshot {}