diff --git a/OpenRA.Game/Traits/Activities/CancelableActivity.cs b/OpenRA.Game/Traits/Activities/CancelableActivity.cs
index 0f6f3ce8f4..d2d4139084 100755
--- a/OpenRA.Game/Traits/Activities/CancelableActivity.cs
+++ b/OpenRA.Game/Traits/Activities/CancelableActivity.cs
@@ -5,24 +5,17 @@ using System.Text;
 
 namespace OpenRA.Traits.Activities
 {
-	public class Activity
+	public abstract class Activity
 	{
 		public Activity NextActivity { get; set; }
 		protected bool IsCanceled { get; private set; }
 
-		public virtual Activity Tick( Actor self )
-		{
-			return this;	
-		}
-		protected virtual bool OnCancel( Actor self ) { return true; }
+		public abstract Activity Tick( Actor self );
 
 		public virtual void Cancel( Actor self )
 		{
-			IsCanceled = OnCancel( self );
-			if( IsCanceled )
-				NextActivity = null;
-			else if (NextActivity != null)
-				NextActivity.Cancel( self );
+			IsCanceled = true;
+			NextActivity = null;
 		}
 
 		public virtual void Queue( Activity activity )
diff --git a/OpenRA.Mods.Cnc/Activities/HarvesterDockSequence.cs b/OpenRA.Mods.Cnc/Activities/HarvesterDockSequence.cs
index 7c4250260a..2be7776aff 100644
--- a/OpenRA.Mods.Cnc/Activities/HarvesterDockSequence.cs
+++ b/OpenRA.Mods.Cnc/Activities/HarvesterDockSequence.cs
@@ -80,10 +80,10 @@ namespace OpenRA.Mods.Cnc
 			throw new InvalidOperationException("Invalid harvester dock state");
 		}
 
-		protected override bool OnCancel(Actor self)
+		public override void Cancel(Actor self)
 		{
 			state = State.Undock;
-			return true;
+			base.Cancel(self);
 		}
 
 		public override IEnumerable<Target> GetTargets( Actor self )
diff --git a/OpenRA.Mods.RA/Activities/CallFunc.cs b/OpenRA.Mods.RA/Activities/CallFunc.cs
index 5b5cc5c05b..0c55263f81 100644
--- a/OpenRA.Mods.RA/Activities/CallFunc.cs
+++ b/OpenRA.Mods.RA/Activities/CallFunc.cs
@@ -33,13 +33,10 @@ namespace OpenRA.Mods.RA.Activities
 			return NextActivity;
 		}
 
-		protected override bool OnCancel(Actor self)
+		public override void Cancel(Actor self)
 		{
-			if (!interruptable)
-				return false;
-			
-			a = null;
-			return true;
+			if (interruptable)
+				base.Cancel(self);
 		}
 	}
 }
diff --git a/OpenRA.Mods.RA/Activities/DeliverOre.cs b/OpenRA.Mods.RA/Activities/DeliverOre.cs
index 50d838e1f1..3a90160c72 100755
--- a/OpenRA.Mods.RA/Activities/DeliverOre.cs
+++ b/OpenRA.Mods.RA/Activities/DeliverOre.cs
@@ -23,6 +23,7 @@ namespace OpenRA.Mods.RA.Activities
 
 		public override Activity Tick( Actor self )
 		{
+			// TODO: wtf is this?
 			if( NextActivity != null )
 				return NextActivity;
 
@@ -48,11 +49,8 @@ namespace OpenRA.Mods.RA.Activities
 			}
 			return Util.SequenceActivities( new Wait(10), this );
 		}
-
-		protected override bool OnCancel(Actor self)
-		{
-			// TODO: allow canceling of deliver orders?
-			return false;
-		}
+		
+		// Cannot be cancelled
+		public override void Cancel(Actor self) { }
 	}
 }
diff --git a/OpenRA.Mods.RA/Activities/MakeAnimation.cs b/OpenRA.Mods.RA/Activities/MakeAnimation.cs
index a471fc96b4..c620c5028b 100644
--- a/OpenRA.Mods.RA/Activities/MakeAnimation.cs
+++ b/OpenRA.Mods.RA/Activities/MakeAnimation.cs
@@ -30,7 +30,6 @@ namespace OpenRA.Mods.RA.Activities
 		bool started = false;
 		public override Activity Tick( Actor self )
 		{
-			if (IsCanceled) return NextActivity;
 			if (!started)
 			{
 				var rb = self.Trait<RenderBuilding>();
@@ -51,7 +50,7 @@ namespace OpenRA.Mods.RA.Activities
 			return complete ? NextActivity : this;
 		}
 		
-		// Not actually cancellable
-		protected override bool OnCancel( Actor self ) { return false; }
+		// Cannot be cancelled
+		public override void Cancel( Actor self ) { }
 	}
 }
diff --git a/OpenRA.Mods.RA/Activities/RAHarvesterDockSequence.cs b/OpenRA.Mods.RA/Activities/RAHarvesterDockSequence.cs
index 7582faa9f1..111d5886a8 100644
--- a/OpenRA.Mods.RA/Activities/RAHarvesterDockSequence.cs
+++ b/OpenRA.Mods.RA/Activities/RAHarvesterDockSequence.cs
@@ -70,10 +70,10 @@ namespace OpenRA.Mods.RA
 			throw new InvalidOperationException("Invalid harvester dock state");
 		}
 
-		protected override bool OnCancel(Actor self)
+		public override void Cancel(Actor self)
 		{
 			state = State.Undock;
-			return true;
+			base.Cancel(self);
 		}
 
 		public override IEnumerable<Target> GetTargets( Actor self )
diff --git a/OpenRA.Mods.RA/Activities/Sell.cs b/OpenRA.Mods.RA/Activities/Sell.cs
index 63d80c7980..db31ff501e 100755
--- a/OpenRA.Mods.RA/Activities/Sell.cs
+++ b/OpenRA.Mods.RA/Activities/Sell.cs
@@ -40,7 +40,7 @@ namespace OpenRA.Mods.RA.Activities
 			return this;
 		}
 
-		// Not actually cancellable
-		protected override bool OnCancel( Actor self ) { return false; }
+		// Cannot be cancelled
+		public override void Cancel( Actor self ) { }
 	}
 }
diff --git a/OpenRA.Mods.RA/Activities/Wait.cs b/OpenRA.Mods.RA/Activities/Wait.cs
index 16e34b795d..e35007294e 100644
--- a/OpenRA.Mods.RA/Activities/Wait.cs
+++ b/OpenRA.Mods.RA/Activities/Wait.cs
@@ -27,15 +27,16 @@ namespace OpenRA.Mods.RA.Activities
 		
 		public override Activity Tick(Actor self)
 		{
-			if (remainingTicks-- == 0) return NextActivity;
-			return this;
+			return (remainingTicks-- == 0) ? NextActivity: this;
 		}
 
-		protected override bool OnCancel( Actor self )
+		public override void Cancel( Actor self )
 		{
-			if( !interruptable ) return false;
+			if( !interruptable )
+				return;
+
 			remainingTicks = 0;
-			return true;
+			base.Cancel(self);
 		}
 	}
 }
diff --git a/OpenRA.Mods.RA/Air/FallsToEarth.cs b/OpenRA.Mods.RA/Air/FallsToEarth.cs
index b89bee350b..b86c28f908 100755
--- a/OpenRA.Mods.RA/Air/FallsToEarth.cs
+++ b/OpenRA.Mods.RA/Air/FallsToEarth.cs
@@ -73,6 +73,7 @@ namespace OpenRA.Mods.RA.Air
 			return this;
 		}
 
-		protected override bool OnCancel(Actor self) { return false; }
+		// Cannot be cancelled
+		public override void Cancel( Actor self ) { }
 	}
 }
diff --git a/OpenRA.Mods.RA/Air/FlyAttack.cs b/OpenRA.Mods.RA/Air/FlyAttack.cs
index f2a4dd8dbd..15162a93b3 100755
--- a/OpenRA.Mods.RA/Air/FlyAttack.cs
+++ b/OpenRA.Mods.RA/Air/FlyAttack.cs
@@ -44,11 +44,12 @@ namespace OpenRA.Mods.RA.Air
 			return this;
 		}
 
-		protected override bool OnCancel( Actor self )
+		public override void Cancel( Actor self )
 		{
 			if( inner != null )
 				inner.Cancel( self );
-			return base.OnCancel( self );
+
+			base.Cancel( self );
 		}
 	}
 
diff --git a/OpenRA.Mods.RA/Air/FlyTimed.cs b/OpenRA.Mods.RA/Air/FlyTimed.cs
index 2815e22a30..02fca8351c 100755
--- a/OpenRA.Mods.RA/Air/FlyTimed.cs
+++ b/OpenRA.Mods.RA/Air/FlyTimed.cs
@@ -36,14 +36,17 @@ namespace OpenRA.Mods.RA.Air
 		public override Activity Tick(Actor self)
 		{
 			var targetAltitude = self.Info.Traits.Get<PlaneInfo>().CruiseAltitude;
-			if (IsCanceled || !self.World.Map.IsInMap(self.Location)) return NextActivity;
+			if (IsCanceled || !self.World.Map.IsInMap(self.Location))
+				return NextActivity;
+
 			FlyUtil.Fly(self, targetAltitude);
 			return this;
 		}
 
-		protected override bool OnCancel( Actor self )
+		public override void Cancel( Actor self )
 		{
-			return Interruptible;
+			if (Interruptible)
+				base.Cancel(self);
 		}
 	}
 }
diff --git a/OpenRA.Mods.RA/AttackMove.cs b/OpenRA.Mods.RA/AttackMove.cs
index e966011e17..2a28d71efa 100644
--- a/OpenRA.Mods.RA/AttackMove.cs
+++ b/OpenRA.Mods.RA/AttackMove.cs
@@ -90,11 +90,12 @@ namespace OpenRA.Mods.RA
 				return this;
 			}
 
-			protected override bool OnCancel( Actor self )
+			public override void Cancel( Actor self )
 			{
 				if( inner != null )
 					inner.Cancel( self );
-				return base.OnCancel( self );
+
+				base.Cancel( self );
 			}
 		}
 	}
diff --git a/OpenRA.Mods.RA/Move/Drag.cs b/OpenRA.Mods.RA/Move/Drag.cs
index 71bf4edfc2..b697c901c2 100755
--- a/OpenRA.Mods.RA/Move/Drag.cs
+++ b/OpenRA.Mods.RA/Move/Drag.cs
@@ -42,14 +42,12 @@ namespace OpenRA.Mods.RA.Move
 			return this;
 		}
 
-		protected override bool OnCancel(Actor self) 
-		{	
-			return false;
-		}
-
 		public override IEnumerable<Target> GetTargets( Actor self )
 		{
 			yield return Target.FromPos(endLocation);
 		}
+
+		// Cannot be cancelled
+		public override void Cancel( Actor self ) { }
 	}
 }
diff --git a/OpenRA.Mods.RA/Move/Move.cs b/OpenRA.Mods.RA/Move/Move.cs
index 14ed6e9b73..d810c5a8d9 100755
--- a/OpenRA.Mods.RA/Move/Move.cs
+++ b/OpenRA.Mods.RA/Move/Move.cs
@@ -233,10 +233,10 @@ namespace OpenRA.Mods.RA.Move
 			return Pair.New(nextCell, subCell);
 		}
 
-		protected override bool OnCancel( Actor self )
+		public override void Cancel( Actor self )
 		{
 			path = new List<int2>();
-			return true;
+			base.Cancel(self);
 		}
 
 		public override IEnumerable<Target> GetTargets( Actor self )
@@ -267,9 +267,10 @@ namespace OpenRA.Mods.RA.Move
 				this.moveFractionTotal = ( ( to - from ) * 3 ).Length;
 			}
 
-			protected override bool OnCancel( Actor self )
+			public override void Cancel( Actor self )
 			{
-				return move.OnCancel( self );
+				move.Cancel( self );
+				base.Cancel( self );
 			}
 
 			public override void Queue( Activity activity )