diff --git a/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj b/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
index 1e481b9144..25b9616c3c 100644
--- a/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
+++ b/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
@@ -872,6 +872,7 @@
     <Compile Include="UpdateRules\Rules\RemovePaletteFromCurrentTileset.cs" />
     <Compile Include="Traits\Player\PlayerResources.cs" />
     <Compile Include="UtilityCommands\DumpSequenceSheetsCommand.cs" />
+    <Compile Include="UpdateRules\Rules\DefineLocomotors.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">
diff --git a/OpenRA.Mods.Common/UpdateRules/Rules/DefineLocomotors.cs b/OpenRA.Mods.Common/UpdateRules/Rules/DefineLocomotors.cs
new file mode 100644
index 0000000000..311f177d9a
--- /dev/null
+++ b/OpenRA.Mods.Common/UpdateRules/Rules/DefineLocomotors.cs
@@ -0,0 +1,163 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2018 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenRA.Mods.Common.UpdateRules.Rules
+{
+	public class DefineLocomotors : UpdateRule
+	{
+		public override string Name { get { return "Introduce global Locomotor definitions"; } }
+		public override string Description
+		{
+			get
+			{
+				return "A large number of properties have been moved from the actor-level Mobile trait\n" +
+					"to either world-level Locomotor traits or new actor-level GrantCondition* traits.\n" +
+					"Conditions for subterranean and jumpjet behaviours are migrated,\n" +
+					"and affected Mobile traits are listed for inspection.";
+			}
+		}
+
+		readonly List<Tuple<string, string>> locations = new List<Tuple<string, string>>();
+		bool subterraneanUsed;
+		bool jumpjetUsed;
+
+		readonly string[] locomotorFields =
+		{
+			"TerrainSpeeds", "Crushes", "CrushDamageTypes", "SharesCell", "MoveIntoShroud"
+		};
+
+		readonly string[] subterraneanFields =
+		{
+			"SubterraneanTransitionCost", "SubterraneanTransitionTerrainTypes",
+			"SubterraneanTransitionOnRamps", "SubterraneanTransitionDepth",
+			"SubterraneanTransitionPalette", "SubterraneanTransitionSound",
+		};
+
+		readonly string[] jumpjetFields =
+		{
+			"JumpjetTransitionCost", "JumpjetTransitionTerrainTypes", "JumpjetTransitionOnRamps"
+		};
+
+		public override IEnumerable<string> AfterUpdate(ModData modData)
+		{
+			var message = "You must define a set of Locomotor traits to the World actor for the different\n"
+				+ "movement classes used in your mod (e.g. Infantry, Vehicles, Tanks, Ships, etc)\n"
+				+ "and replace any definitions/overrides of the following properties on each\n"
+				+ "actor with a Locomotor field referencing the appropriate locomotor type.\n\n"
+				+ "The standard Locomotor definition contains the following fields:\n"
+				+ UpdateUtils.FormatMessageList(locomotorFields) + "\n\n";
+
+			if (subterraneanUsed)
+				message += "Actors using the subterranean logic should reference a SubterraneanLocomotor\n"
+				+ "instance that extends Locomotor with additional fields:\n"
+				+ UpdateUtils.FormatMessageList(subterraneanFields) + "\n\n";
+
+			if (jumpjetUsed)
+				message += "Actors using the jump-jet logic should reference a JumpjetLocomotor\n"
+				+ "instance that extends Locomotor with additional fields:\n"
+				+ UpdateUtils.FormatMessageList(jumpjetFields) + "\n\n";
+
+			message += "Condition definitions have been automatically migrated.\n"
+				+ "The following definitions reference fields that must be manually moved to Locomotors:\n"
+				+ UpdateUtils.FormatMessageList(locations.Select(n => n.Item1 + " (" + n.Item2 + ")"));
+
+			if (locations.Any())
+				yield return message;
+
+			locations.Clear();
+		}
+
+		public override IEnumerable<string> UpdateActorNode(ModData modData, MiniYamlNode actorNode)
+		{
+			var addNodes = new List<MiniYamlNode>();
+			foreach (var mobileNode in actorNode.ChildrenMatching("Mobile"))
+			{
+				var checkFields = locomotorFields.Append(subterraneanFields).Append(jumpjetFields);
+				if (checkFields.Any(f => mobileNode.ChildrenMatching(f).Any()))
+					locations.Add(Tuple.Create(actorNode.Key, actorNode.Location.Filename));
+
+				var tunnelConditionNode = mobileNode.LastChildMatching("TunnelCondition");
+				if (tunnelConditionNode != null)
+				{
+					var grantNode = new MiniYamlNode("GrantConditionOnTunnelLayer", "");
+					grantNode.AddNode("Condition", tunnelConditionNode.Value.Value);
+					addNodes.Add(grantNode);
+					mobileNode.RemoveNodes("TunnelCondition");
+				}
+
+				var subterraneanNode = mobileNode.LastChildMatching("Subterranean");
+				if (subterraneanNode != null)
+				{
+					subterraneanUsed = true;
+
+					mobileNode.RemoveNodes("Subterranean");
+					var conditionNode = mobileNode.LastChildMatching("SubterraneanCondition");
+					if (conditionNode != null)
+						conditionNode.RenameKeyPreservingSuffix("Condition");
+
+					var transitionImageNode = mobileNode.LastChildMatching("SubterraneanTransitionImage");
+					var transitionSequenceNode = mobileNode.LastChildMatching("SubterraneanTransitionSequence");
+					var transitionPaletteNode = mobileNode.LastChildMatching("SubterraneanTransitionPalette");
+					var transitionSoundNode = mobileNode.LastChildMatching("SubterraneanTransitionSound");
+
+					var nodes = new[]
+					{
+						conditionNode,
+						transitionImageNode,
+						transitionSequenceNode,
+						transitionPaletteNode,
+						transitionSoundNode
+					};
+
+					if (nodes.Any(n => n != null))
+					{
+						var grantNode = new MiniYamlNode("GrantConditionOnSubterraneanLayer", "");
+						foreach (var node in nodes)
+						{
+							if (node != null)
+							{
+								grantNode.Value.Nodes.Add(node);
+								mobileNode.Value.Nodes.Remove(node);
+							}
+						}
+
+						addNodes.Add(grantNode);
+					}
+				}
+
+				var jumpjetNode = mobileNode.LastChildMatching("Jumpjet");
+				if (jumpjetNode != null)
+				{
+					jumpjetUsed = true;
+
+					mobileNode.RemoveNodes("Jumpjet");
+					var conditionNode = mobileNode.LastChildMatching("JumpjetCondition");
+					if (conditionNode != null)
+					{
+						var grantNode = new MiniYamlNode("GrantConditionOnJumpjetLayer", "");
+						grantNode.AddNode("Condition", conditionNode.Value.Value);
+						mobileNode.RemoveNodes("JumpjetCondition");
+						addNodes.Add(grantNode);
+					}
+				}
+			}
+
+			foreach (var node in addNodes)
+				actorNode.Value.Nodes.Add(node);
+
+			yield break;
+		}
+	}
+}