diff --git a/core/assets/bundles/bundle.properties b/core/assets/bundles/bundle.properties
index f19fceafef..3e9976024d 100644
--- a/core/assets/bundles/bundle.properties
+++ b/core/assets/bundles/bundle.properties
@@ -123,6 +123,7 @@ text.server.port=Port:
 text.server.addressinuse=Address already in use!
 text.server.invalidport=Invalid port number!
 text.server.error=[crimson]Error hosting server: [orange]{0}
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
 text.save.new=New Save
 text.save.overwrite=Are you sure you want to overwrite\nthis save slot?
 text.overwrite=Overwrite
@@ -292,7 +293,6 @@ text.blocks.inputfuel=Fuel
 text.blocks.fuelburntime=Fuel Burn Time
 text.blocks.inputcapacity=Input capacity
 text.blocks.outputcapacity=Output capacity
-text.blocks.required=Required:
 
 text.unit.blocks=blocks
 text.unit.powersecond=power units/second
diff --git a/core/assets/bundles/bundle_de.properties b/core/assets/bundles/bundle_de.properties
index 23c3f886eb..78b1bf4794 100644
--- a/core/assets/bundles/bundle_de.properties
+++ b/core/assets/bundles/bundle_de.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_es.properties b/core/assets/bundles/bundle_es.properties
index 9ee631d3ab..a8136b7ead 100644
--- a/core/assets/bundles/bundle_es.properties
+++ b/core/assets/bundles/bundle_es.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_fr.properties b/core/assets/bundles/bundle_fr.properties
index e1ee0c31a7..4d29faf7f7 100644
--- a/core/assets/bundles/bundle_fr.properties
+++ b/core/assets/bundles/bundle_fr.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_in_ID.properties b/core/assets/bundles/bundle_in_ID.properties
index 9f1ec1436f..b4c7f1e2a4 100644
--- a/core/assets/bundles/bundle_in_ID.properties
+++ b/core/assets/bundles/bundle_in_ID.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_ita.properties b/core/assets/bundles/bundle_ita.properties
index 93cb8a4f36..4b02d88130 100644
--- a/core/assets/bundles/bundle_ita.properties
+++ b/core/assets/bundles/bundle_ita.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_ko.properties b/core/assets/bundles/bundle_ko.properties
index 3b3f145bd3..6169edd949 100644
--- a/core/assets/bundles/bundle_ko.properties
+++ b/core/assets/bundles/bundle_ko.properties
@@ -492,3 +492,4 @@ block.distributor.name=Distributor
 block.distributor.description=A splitter that can split items into 8 directions.
 block.overflow-gate.description=A combination splitter and router that only outputs to the left and right if the front path is blocked.
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_pl.properties b/core/assets/bundles/bundle_pl.properties
index 1336e0650b..ef022067b0 100644
--- a/core/assets/bundles/bundle_pl.properties
+++ b/core/assets/bundles/bundle_pl.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_pt_BR.properties b/core/assets/bundles/bundle_pt_BR.properties
index 04f28bf94a..3b54e1282d 100644
--- a/core/assets/bundles/bundle_pt_BR.properties
+++ b/core/assets/bundles/bundle_pt_BR.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_ru.properties b/core/assets/bundles/bundle_ru.properties
index 1d14c9c417..81593c7e58 100644
--- a/core/assets/bundles/bundle_ru.properties
+++ b/core/assets/bundles/bundle_ru.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_tk.properties b/core/assets/bundles/bundle_tk.properties
index 6120e00fd3..b8006f0edb 100644
--- a/core/assets/bundles/bundle_tk.properties
+++ b/core/assets/bundles/bundle_tk.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/assets/bundles/bundle_uk_UA.properties b/core/assets/bundles/bundle_uk_UA.properties
index ecc5320001..7a85ec0af1 100644
--- a/core/assets/bundles/bundle_uk_UA.properties
+++ b/core/assets/bundles/bundle_uk_UA.properties
@@ -492,3 +492,4 @@ block.liquid-junction.name=Liquid Junction
 block.bridge-conduit.name=Bridge Conduit
 block.rotary-pump.name=Rotary Pump
 block.nuclear-reactor.name=Nuclear Reactor
+text.save.old=This save is for an older version of the game, and can no longer be used.\n\n[LIGHT_GRAY]Save backwards compatibility will be implemented in the full 4.0 release.
diff --git a/core/src/io/anuke/mindustry/entities/units/FlyingUnit.java b/core/src/io/anuke/mindustry/entities/units/FlyingUnit.java
index cdcdbf4717..1b2df0d94c 100644
--- a/core/src/io/anuke/mindustry/entities/units/FlyingUnit.java
+++ b/core/src/io/anuke/mindustry/entities/units/FlyingUnit.java
@@ -23,9 +23,13 @@ import static io.anuke.mindustry.Vars.world;
 public abstract class FlyingUnit extends BaseUnit implements CarryTrait{
     protected static Translator vec = new Translator();
     protected static float wobblyness = 0.6f;
-    public final UnitState
 
-            resupply = new UnitState(){
+    protected Trail trail = new Trail(8);
+    protected CarriableTrait carrying;
+
+    protected final UnitState
+
+    resupply = new UnitState(){
         public void entered(){
             target = null;
         }
@@ -40,81 +44,79 @@ public abstract class FlyingUnit extends BaseUnit implements CarryTrait{
             }
         }
     },
-            idle = new UnitState(){
-                public void update(){
-                    retarget(() -> {
-                        targetClosest();
-                        targetClosestEnemyFlag(BlockFlag.target);
+    idle = new UnitState(){
+        public void update(){
+            retarget(() -> {
+                targetClosest();
+                targetClosestEnemyFlag(BlockFlag.target);
 
-                        if(target != null){
-                            setState(attack);
-                        }
-                    });
+                if(target != null){
+                    setState(attack);
+                }
+            });
 
-                    target = getClosestCore();
-                    if(target != null){
-                        circle(50f);
+            target = getClosestCore();
+            if(target != null){
+                circle(50f);
+            }
+            velocity.scl(0.8f);
+        }
+    },
+    attack = new UnitState(){
+        public void entered(){
+            target = null;
+        }
+
+        public void update(){
+            if(Units.invalidateTarget(target, team, x, y)){
+                target = null;
+            }
+
+            if(!inventory.hasAmmo()){
+                state.set(resupply);
+            }else if(target == null){
+                retarget(() -> {
+                    targetClosest();
+                    targetClosestEnemyFlag(BlockFlag.target);
+                    targetClosestEnemyFlag(BlockFlag.producer);
+
+                    if(target == null){
+                        setState(idle);
                     }
-                    velocity.scl(0.8f);
-                }
-            },
-            attack = new UnitState(){
-                public void entered(){
-                    target = null;
+                });
+            }else{
+                attack(150f);
+
+                if((Mathf.angNear(angleTo(target), rotation, 15f) || !inventory.getAmmo().bullet.keepVelocity) //bombers don't care about rotation
+                        && distanceTo(target) < inventory.getAmmo().getRange()){
+                    AmmoType ammo = inventory.getAmmo();
+                    inventory.useAmmo();
+
+                    Vector2 to = Predict.intercept(FlyingUnit.this, target, ammo.bullet.speed);
+
+                    getWeapon().update(FlyingUnit.this, to.x, to.y);
                 }
+            }
+        }
+    },
+    retreat = new UnitState(){
+        public void entered(){
+            target = null;
+        }
 
-                public void update(){
-                    if(Units.invalidateTarget(target, team, x, y)){
-                        target = null;
-                    }
-
-                    if(!inventory.hasAmmo()){
-                        state.set(resupply);
-                    }else if(target == null){
-                        retarget(() -> {
-                            targetClosest();
-                            targetClosestEnemyFlag(BlockFlag.target);
-                            targetClosestEnemyFlag(BlockFlag.producer);
-
-                            if(target == null){
-                                setState(idle);
-                            }
-                        });
-                    }else{
-                        attack(150f);
-
-                        if((Mathf.angNear(angleTo(target), rotation, 15f) || !inventory.getAmmo().bullet.keepVelocity) //bombers don't care about rotation
-                                && distanceTo(target) < inventory.getAmmo().getRange()){
-                            AmmoType ammo = inventory.getAmmo();
-                            inventory.useAmmo();
-
-                            Vector2 to = Predict.intercept(FlyingUnit.this, target, ammo.bullet.speed);
-
-                            getWeapon().update(FlyingUnit.this, to.x, to.y);
-                        }
-                    }
-                }
-            },
-            retreat = new UnitState(){
-                public void entered(){
-                    target = null;
-                }
-
-                public void update(){
-                    if(health >= maxHealth()){
-                        state.set(attack);
-                    }else if(!targetHasFlag(BlockFlag.repair)){
-                        retarget(() -> {
-                            Tile target = Geometry.findClosest(x, y, world.indexer().getAllied(team, BlockFlag.repair));
-                            if(target != null) FlyingUnit.this.target = target.entity;
-                        });
-                    }else{
-                        circle(20f);
-                    }
-                }
-            };
-    protected Trail trail = new Trail(8);
-    protected CarriableTrait carrying;
+        public void update(){
+            if(health >= maxHealth()){
+                state.set(attack);
+            }else if(!targetHasFlag(BlockFlag.repair)){
+                retarget(() -> {
+                    Tile target = Geometry.findClosest(x, y, world.indexer().getAllied(team, BlockFlag.repair));
+                    if(target != null) FlyingUnit.this.target = target.entity;
+                });
+            }else{
+                circle(20f);
+            }
+        }
+    };
 
     //instantiation only
     public FlyingUnit(){
diff --git a/core/src/io/anuke/mindustry/io/SaveFileVersion.java b/core/src/io/anuke/mindustry/io/SaveFileVersion.java
index 48ec0b58e8..4a66242dfd 100644
--- a/core/src/io/anuke/mindustry/io/SaveFileVersion.java
+++ b/core/src/io/anuke/mindustry/io/SaveFileVersion.java
@@ -15,11 +15,12 @@ public abstract class SaveFileVersion{
 
     public SaveMeta getData(DataInputStream stream) throws IOException{
         long time = stream.readLong(); //read last saved time
+        int build = stream.readInt();
         byte mode = stream.readByte(); //read the gamemode
         String map = stream.readUTF(); //read the map
         int wave = stream.readInt(); //read the wave
         byte difficulty = stream.readByte(); //read the difficulty
-        return new SaveMeta(version, time, mode, map, wave, Difficulty.values()[difficulty]);
+        return new SaveMeta(version, time, build, mode, map, wave, Difficulty.values()[difficulty]);
     }
 
     public abstract void read(DataInputStream stream) throws IOException;
diff --git a/core/src/io/anuke/mindustry/io/SaveIO.java b/core/src/io/anuke/mindustry/io/SaveIO.java
index bfe652c384..98ed4b251c 100644
--- a/core/src/io/anuke/mindustry/io/SaveIO.java
+++ b/core/src/io/anuke/mindustry/io/SaveIO.java
@@ -3,6 +3,7 @@ package io.anuke.mindustry.io;
 import com.badlogic.gdx.files.FileHandle;
 import com.badlogic.gdx.utils.Array;
 import com.badlogic.gdx.utils.Base64Coder;
+import com.badlogic.gdx.utils.IntArray;
 import com.badlogic.gdx.utils.IntMap;
 import io.anuke.mindustry.Vars;
 import io.anuke.mindustry.io.versions.Save16;
@@ -15,9 +16,10 @@ import java.util.zip.InflaterInputStream;
 import static io.anuke.mindustry.Vars.*;
 
 public class SaveIO{
+    public static final IntArray breakingVersions = IntArray.with(47);
     public static final IntMap<SaveFileVersion> versions = new IntMap<>();
     public static final Array<SaveFileVersion> versionArray = Array.with(
-            new Save16()
+        new Save16()
     );
 
     static{
diff --git a/core/src/io/anuke/mindustry/io/SaveMeta.java b/core/src/io/anuke/mindustry/io/SaveMeta.java
index 5fd655f6b2..f782e74db1 100644
--- a/core/src/io/anuke/mindustry/io/SaveMeta.java
+++ b/core/src/io/anuke/mindustry/io/SaveMeta.java
@@ -10,14 +10,16 @@ import static io.anuke.mindustry.Vars.world;
 
 public class SaveMeta{
     public int version;
+    public int build;
     public String date;
     public GameMode mode;
     public Map map;
     public int wave;
     public Difficulty difficulty;
 
-    public SaveMeta(int version, long date, int mode, String map, int wave, Difficulty difficulty){
+    public SaveMeta(int version, long date, int build, int mode, String map, int wave, Difficulty difficulty){
         this.version = version;
+        this.build = build;
         this.date = Platform.instance.format(new Date(date));
         this.mode = GameMode.values()[mode];
         this.map = world.maps().getByName(map);
diff --git a/core/src/io/anuke/mindustry/io/Saves.java b/core/src/io/anuke/mindustry/io/Saves.java
index 4096974e97..0fd1792034 100644
--- a/core/src/io/anuke/mindustry/io/Saves.java
+++ b/core/src/io/anuke/mindustry/io/Saves.java
@@ -144,6 +144,10 @@ public class Saves{
             Settings.save();
         }
 
+        public int getBuild(){
+            return meta.build;
+        }
+
         public int getWave(){
             return meta.wave;
         }
diff --git a/core/src/io/anuke/mindustry/io/versions/Save16.java b/core/src/io/anuke/mindustry/io/versions/Save16.java
index ece1178776..afe056970c 100644
--- a/core/src/io/anuke/mindustry/io/versions/Save16.java
+++ b/core/src/io/anuke/mindustry/io/versions/Save16.java
@@ -11,6 +11,7 @@ import io.anuke.mindustry.game.GameMode;
 import io.anuke.mindustry.game.Team;
 import io.anuke.mindustry.io.Map;
 import io.anuke.mindustry.io.SaveFileVersion;
+import io.anuke.mindustry.io.Version;
 import io.anuke.mindustry.world.Block;
 import io.anuke.mindustry.world.Tile;
 import io.anuke.mindustry.world.blocks.BlockPart;
@@ -153,6 +154,7 @@ public class Save16 extends SaveFileVersion{
         //--META--
         stream.writeInt(version); //version id
         stream.writeLong(TimeUtils.millis()); //last saved
+        stream.writeInt(Version.build);
 
         //--GENERAL STATE--
         stream.writeByte(state.mode.ordinal()); //gamemode
@@ -175,7 +177,6 @@ public class Save16 extends SaveFileVersion{
         }
 
         //--ENTITIES--
-        //TODO synchronized block here
 
         int groups = 0;
 
diff --git a/core/src/io/anuke/mindustry/ui/dialogs/LoadDialog.java b/core/src/io/anuke/mindustry/ui/dialogs/LoadDialog.java
index 03fb0ffdee..529c48ff73 100644
--- a/core/src/io/anuke/mindustry/ui/dialogs/LoadDialog.java
+++ b/core/src/io/anuke/mindustry/ui/dialogs/LoadDialog.java
@@ -185,7 +185,13 @@ public class LoadDialog extends FloatingDialog{
     public void modifyButton(TextButton button, SaveSlot slot){
         button.clicked(() -> {
             if(!button.childrenPressed()){
-                runLoadSave(slot);
+                int build = slot.getBuild();
+                if(SaveIO.breakingVersions.contains(build)){
+                    ui.showInfo("$text.save.old");
+                    slot.delete();
+                }else{
+                    runLoadSave(slot);
+                }
             }
         });
     }