diff --git a/OpenRa.Game/GameRules/NewUnitInfo.cs b/OpenRa.Game/GameRules/NewUnitInfo.cs
index 1f84bce4e0..3c44f45762 100755
--- a/OpenRa.Game/GameRules/NewUnitInfo.cs
+++ b/OpenRa.Game/GameRules/NewUnitInfo.cs
@@ -24,7 +24,7 @@ namespace OpenRa.Game.GameRules
 		{
 			MiniYaml inherits;
 			node.Nodes.TryGetValue( "Inherits", out inherits );
-			if( inherits.Value == null || string.IsNullOrEmpty( inherits.Value ) )
+			if( inherits == null || string.IsNullOrEmpty( inherits.Value ) )
 				return node;
 
 			MiniYaml parent;
diff --git a/RulesConverter/Program.cs b/RulesConverter/Program.cs
index c47863ec82..e9cda7e9f1 100644
--- a/RulesConverter/Program.cs
+++ b/RulesConverter/Program.cs
@@ -85,6 +85,7 @@ namespace RulesConverter
 					{ "TechLevel", "TechLevel" },
 					{ "Tab", "$Tab" },
 					{ "@Prerequisites", "Prerequisite" },
+					{ "BuiltAt", "BuiltAt" },
 					{ "Owner", "Owner" },
 					{ "Cost", "Cost" },
 					{ "Icon", "Icon" },
diff --git a/aftermath.yaml b/aftermath.yaml
index 5eaff6733b..05fe317ae1 100644
--- a/aftermath.yaml
+++ b/aftermath.yaml
@@ -116,6 +116,7 @@ MSUB:
 		TechLevel: 9
 		Tab: Ship
 		Prerequisites: stek
+		BuiltAt: spen
 		Owner: soviet
 		Cost: 1650
 		Description: "Missile Submarine"
diff --git a/ra.yaml b/ra.yaml
index 5575716221..73332b05b2 100644
--- a/ra.yaml
+++ b/ra.yaml
@@ -443,6 +443,7 @@ SS:
 		TechLevel: 5
 		Tab: Ship
 		Prerequisites: spen
+		BuiltAt: spen
 		Owner: soviet
 		Cost: 950
 		Description: "Submarine"
@@ -469,6 +470,7 @@ DD:
 		TechLevel: 7
 		Tab: Ship
 		Prerequisites: syrd
+		BuiltAt: syrd
 		Owner: allies
 		Cost: 1000
 		Description: "Destroyer"
@@ -496,6 +498,7 @@ CA:
 		TechLevel: 10
 		Tab: Ship
 		Prerequisites: syrd,atek
+		BuiltAt: syrd
 		Owner: allies
 		Cost: 2000
 		Description: "Cruiser"
@@ -548,6 +551,7 @@ PT:
 		TechLevel: 5
 		Tab: Ship
 		Prerequisites: syrd
+		BuiltAt: syrd
 		Owner: allies
 		Cost: 500
 		Description: "Gunboat"
@@ -575,6 +579,7 @@ MIG:
 		TechLevel: 10
 		Tab: Plane
 		Prerequisites: afld
+		BuiltAt: afld
 		Owner: soviet
 		Cost: 1200
 		Description: "Mig Attack Plane"
@@ -602,6 +607,7 @@ YAK:
 		TechLevel: 5
 		Tab: Plane
 		Prerequisites: afld
+		BuiltAt: afld
 		Owner: soviet
 		Cost: 800
 		Description: "Yak Attack Plane"
@@ -630,6 +636,7 @@ TRAN:
 		TechLevel: 11
 		Tab: Plane
 		Prerequisites: hpad
+		BuiltAt: hpad
 		Owner: allies
 		Cost: 1200
 		Description: "Transport Helicopter"
@@ -658,6 +665,7 @@ HELI:
 		TechLevel: 9
 		Tab: Plane
 		Prerequisites: hpad
+		BuiltAt: hpad
 		Owner: allies
 		Cost: 1200
 		Description: "Longbow"
@@ -689,6 +697,7 @@ HIND:
 		TechLevel: 9
 		Tab: Plane
 		Prerequisites: hpad
+		BuiltAt: hpad
 		Owner: allies
 		Cost: 1200
 		Description: "Hind"
@@ -2234,6 +2243,7 @@ DOG:
 		TechLevel: 3
 		Tab: Infantry
 		Prerequisites: kenn
+		BuiltAt: KENN
 		Owner: soviet
 		Cost: 200
 		Description: "Attack Dog"