O
- OA. UK (Thames) Outbound 1939-41
- OB. UK (Liverpool) Outbound 1939-41
- OC. Melbourne to Newcastle (reverse CO)
- OG. UK ("outbound") to Gibraltar (reverse HG)
- OM. Oran to Marseilles 1944 (reverse MO)
- ON. Methil to Bergen ("Outbound Norway") 1939-40
- ON. UK to North America 1941-45 North Atlantic route; this series ran alternately Fast and Slow but after 1943 Fast only
- ON(F) Fast ON 1941-43 (reverse HX)
- ON(S) Slow ON 1941-43 (reverse SC)
- ONS. UK to North America 1943-45 North Atlantic route, replaced ON(S) (reverse SC)
- OS. Liverpool to Freetown ("Outbound South")
- OSS. continuation of OS route south
- OT. Trinidad to North Africa ("Outbound Trinidad")
- OT. Trinidad to Caribbean local ("Outbound Trinidad")
- OW. Australia to India ("Outbound West")
Read more about this topic: List Of World War II Convoy Codes