diff --git a/OpenRA.Mods.Common/Scripting/Global/TriggerGlobal.cs b/OpenRA.Mods.Common/Scripting/Global/TriggerGlobal.cs
index e64fe77646..5085a319d5 100644
--- a/OpenRA.Mods.Common/Scripting/Global/TriggerGlobal.cs
+++ b/OpenRA.Mods.Common/Scripting/Global/TriggerGlobal.cs
@@ -406,6 +406,20 @@ namespace OpenRA.Mods.Common.Scripting
 			GetScriptTriggers(a).RegisterCallback(Trigger.OnInfiltrated, func, Context);
 		}
 
+		[Desc("Call a function when this actor is discovered by an enemy or a player with a Neutral stance. " +
+			"The callback function will be called as func(Actor discovered, Player discoverer)")]
+		public void OnDiscovered(Actor a, LuaFunction func)
+		{
+			GetScriptTriggers(a).RegisterCallback(Trigger.OnDiscovered, func, Context);
+		}
+
+		[Desc("Call a function when this player is discovered by an enemy or neutral player. " +
+			"The callback function will be called as func(Player discovered, Player discoverer, Actor discoveredActor)")]
+		public void OnPlayerDiscovered(Player discovered, LuaFunction func)
+		{
+			GetScriptTriggers(discovered.PlayerActor).RegisterCallback(Trigger.OnPlayerDiscovered, func, Context);
+		}
+
 		[Desc("Removes all triggers from this actor." +
 			"Note that the removal will only take effect at the end of a tick, " +
 			"so you must not add new triggers at the same time that you are calling this function.")]
diff --git a/OpenRA.Mods.Common/Scripting/ScriptTriggers.cs b/OpenRA.Mods.Common/Scripting/ScriptTriggers.cs
index 3c887b6028..298cb806fb 100644
--- a/OpenRA.Mods.Common/Scripting/ScriptTriggers.cs
+++ b/OpenRA.Mods.Common/Scripting/ScriptTriggers.cs
@@ -21,7 +21,8 @@ namespace OpenRA.Mods.Common.Scripting
 	public enum Trigger
 	{
 		OnIdle, OnDamaged, OnKilled, OnProduction, OnOtherProduction, OnPlayerWon, OnPlayerLost,
-		OnObjectiveAdded, OnObjectiveCompleted, OnObjectiveFailed, OnCapture, OnInfiltrated, OnAddedToWorld, OnRemovedFromWorld
+		OnObjectiveAdded, OnObjectiveCompleted, OnObjectiveFailed, OnCapture, OnInfiltrated,
+		OnAddedToWorld, OnRemovedFromWorld, OnDiscovered, OnPlayerDiscovered
 	}
 
 	[Desc("Allows map scripts to attach triggers to this actor via the Triggers global.")]
@@ -31,7 +32,7 @@ namespace OpenRA.Mods.Common.Scripting
 	}
 
 	public sealed class ScriptTriggers : INotifyIdle, INotifyDamage, INotifyKilled, INotifyProduction, INotifyOtherProduction,
-		INotifyObjectivesUpdated, INotifyCapture, INotifyInfiltrated, INotifyAddedToWorld, INotifyRemovedFromWorld, IDisposable
+		INotifyObjectivesUpdated, INotifyCapture, INotifyInfiltrated, INotifyAddedToWorld, INotifyRemovedFromWorld, IDisposable, INotifyDiscovered
 	{
 		readonly World world;
 
@@ -324,6 +325,40 @@ namespace OpenRA.Mods.Common.Scripting
 			OnOtherProducedInternal(producee, produced);
 		}
 
+		public void OnDiscovered(Actor self, Player discoverer, bool playNotification)
+		{
+			foreach (var f in Triggers[Trigger.OnDiscovered])
+			{
+				try
+				{
+					using (var a = self.ToLuaValue(f.Second))
+					using (var b = discoverer.ToLuaValue(f.Second))
+						f.First.Call(a, b).Dispose();
+				}
+				catch (Exception ex)
+				{
+					f.Second.FatalError(ex.Message);
+					return;
+				}
+			}
+
+			foreach (var f in Triggers[Trigger.OnPlayerDiscovered])
+			{
+				try
+				{
+					using (var a = self.Owner.ToLuaValue(f.Second))
+					using (var b = discoverer.ToLuaValue(f.Second))
+					using (var c = self.ToLuaValue(f.Second))
+						f.First.Call(a, b, c).Dispose();
+				}
+				catch (Exception ex)
+				{
+					f.Second.FatalError(ex.Message);
+					return;
+				}
+			}
+		}
+
 		public void Clear(Trigger trigger)
 		{
 			world.AddFrameEndTask(w =>
diff --git a/mods/cnc/maps/gdi05a/gdi05a.lua b/mods/cnc/maps/gdi05a/gdi05a.lua
index bb26935e74..beb5b8db88 100644
--- a/mods/cnc/maps/gdi05a/gdi05a.lua
+++ b/mods/cnc/maps/gdi05a/gdi05a.lua
@@ -11,11 +11,6 @@ GdiTanks = { "mtnk", "mtnk" }
 GdiApc = { "apc" }
 GdiInfantry = { "e1", "e1", "e1", "e1", "e1", "e2", "e2", "e2", "e2", "e2" }
 GdiBase = { GdiNuke1, GdiNuke2, GdiProc, GdiSilo1, GdiSilo2, GdiPyle, GdiWeap, GdiHarv }
-GdiBaseDiscoveryTrigger =
-{
-	CPos.New(39, 54), CPos.New(48, 42), CPos.New(49, 42), CPos.New(50, 42), CPos.New(51, 42),
-	CPos.New(52, 42), CPos.New(53, 42), CPos.New(54, 42), CPos.New(55, 42), CPos.New(56, 42)
-}
 NodSams = { Sam1, Sam2, Sam3, Sam4 }
 CoreNodBase = { NodConYard, NodRefinery, HandOfNod, Airfield }
 
@@ -122,7 +117,11 @@ Grd3Action = function()
 	end
 end
 
-DiscoverGdiBase = function()
+DiscoverGdiBase = function(actor, discoverer)
+	if baseDiscovered or not discoverer == gdi then
+		return
+	end
+
 	Utils.Do(GdiBase, function(actor)
 		actor.Owner = gdi
 	end)
@@ -145,12 +144,7 @@ SetupWorld = function()
 	Reinforcements.Reinforce(gdi, GdiApc, { GdiApcEntry.Location, GdiApcRallyPoint.Location }, DateTime.Seconds(1), function(actor) actor.Stance = "Defend" end)
 	Reinforcements.Reinforce(gdi, GdiInfantry, { GdiInfantryEntry.Location, GdiInfantryRallyPoint.Location }, 15, function(actor) actor.Stance = "Defend" end)
 
-	Trigger.OnEnteredFootprint(GdiBaseDiscoveryTrigger, function(actor, id)
-		if actor.Owner == gdi then
-			DiscoverGdiBase()
-			Trigger.RemoveFootprintTrigger(id)
-		end
-	end)
+	Trigger.OnPlayerDiscovered(gdiBase, DiscoverGdiBase)
 
 	Utils.Do(Map.NamedActors, function(actor)
 		if actor.Owner == nod and actor.HasProperty("StartBuildingRepairs") then
@@ -186,6 +180,7 @@ SetupWorld = function()
 end
 
 WorldLoaded = function()
+	gdiBase = Player.GetPlayer("AbandonedBase")
 	gdi = Player.GetPlayer("GDI")
 	nod = Player.GetPlayer("Nod")
 
diff --git a/mods/cnc/maps/gdi05a/map.yaml b/mods/cnc/maps/gdi05a/map.yaml
index 47703b3908..4b62f85ebf 100644
--- a/mods/cnc/maps/gdi05a/map.yaml
+++ b/mods/cnc/maps/gdi05a/map.yaml
@@ -2,7 +2,7 @@ MapFormat: 7
 
 RequiresMod: cnc
 
-Title: Repair the GDI base
+Title: Repair the GDI base (a)
 
 Description: A GDI field base is under attack. They have fended off one attack but will not survive another.\n\nMove to the base, repair the structures and then launch a strike force to destroy the Nod base in the area.\n\nDestroy all Nod units and structures.
 
@@ -56,6 +56,11 @@ Players:
 		LockTeam: True
 		Allies: GDI
 		Enemies: Nod
+	PlayerReference@AbandonedBase:
+		Name: AbandonedBase
+		NonCombatant: True
+		ColorRamp: 31,222,183
+		Race: gdi
 	PlayerReference@Neutral:
 		Name: Neutral
 		OwnsWorld: True
@@ -684,36 +689,36 @@ Actors:
 		Owner: Neutral
 	GdiProc: proc
 		Location: 50,51
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.3085938
 		FreeActor: False
 	GdiHarv: harv
 		Location: 48,53
-		Owner: Neutral
+		Owner: AbandonedBase
 		Facing: 64
 	GdiWeap: weap
 		Location: 50,54
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.2695313
 	GdiNuke1: nuke
 		Location: 53,55
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.2890625
 	GdiPyle: pyle
 		Location: 46,55
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.25
 	GdiSilo1: silo
 		Location: 53,51
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.3320313
 	GdiSilo2: silo
 		Location: 53,53
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.25
 	GdiNuke2: nuke
 		Location: 48,56
-		Owner: Neutral
+		Owner: AbandonedBase
 		Health: 0.2070313
 	NodConYard: fact
 		Location: 9,29
@@ -796,6 +801,7 @@ Rules:
 		-ConquestVictoryConditions:
 		MissionObjectives:
 			EarlyGameOver: true
+		EnemyWatcher:
 	^Vehicle:
 		Tooltip:
 			GenericVisibility: Enemy
@@ -826,6 +832,7 @@ Rules:
 		Tooltip:
 			GenericVisibility: Enemy
 			ShowOwnerRow: false
+		AnnounceOnSeen:
 	^Wall:
 		Tooltip:
 			ShowOwnerRow: false