diff --git a/data/target_ships/target_ship_1.json b/data/target_ships/target_ship_1.json
index f1c730b..be1b53a 100644
--- a/data/target_ships/target_ship_1.json
+++ b/data/target_ships/target_ship_1.json
@@ -4,8 +4,7 @@
         "width": 20,
         "height": 8,
         "speedMax": 17,
-        "mmsi": 257845600,
-        "name": "BASTO IV",
+        "name": "BASTO",
         "shipType": "Passenger/Ro-Ro Cargo Ship"
     }
-}
+}
\ No newline at end of file
diff --git a/data/target_ships/target_ship_2.json b/data/target_ships/target_ship_2.json
index 96b4eda..456ca81 100644
--- a/data/target_ships/target_ship_2.json
+++ b/data/target_ships/target_ship_2.json
@@ -4,8 +4,7 @@
         "width": 10,
         "height": 8,
         "speedMax": 15,
-        "mmsi": 257083180,
         "name": "CANOLE",
         "shipType": "Cargo"
     }
-}
+}
\ No newline at end of file
diff --git a/data/target_ships/target_ship_3.json b/data/target_ships/target_ship_3.json
index dbf5408..e22d3bd 100644
--- a/data/target_ships/target_ship_3.json
+++ b/data/target_ships/target_ship_3.json
@@ -4,8 +4,7 @@
         "width": 30,
         "height": 30,
         "speedMax": 21,
-        "mmsi": 219945000,
         "name": "BASTO VI",
         "shipType": "Passenger/Ro-Ro Cargo Ship"
     }
-}
+}
\ No newline at end of file
diff --git a/src/trafficgen/types.py b/src/trafficgen/types.py
index a168c58..8a12874 100644
--- a/src/trafficgen/types.py
+++ b/src/trafficgen/types.py
@@ -1,10 +1,10 @@
 """Domain specific data types used in trafficgen."""
 
 from enum import Enum
-from typing import List, Union
+from typing import List, Optional, Union
 from uuid import UUID
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 
 def to_camel(string: str) -> str:
@@ -99,7 +99,7 @@ class ShipStatic(BaseModel):
     width: float
     height: float
     speed_max: float
-    mmsi: int
+    mmsi: Optional[int] = Field(None, ge=100000000, le=999999999, description="Maritime Mobile Service Identity (MMSI)", examples=[123456789])
     name: str
     ship_type: GeneralShipType