The Designations of Steamers or Steamships (Merchant Vessels)
- S.S. for Steamship (Steam Ship) This is the default designation
- R.M.S. for Royal Mail Ship / Royal Mail Steamer
- M.S. for Motor Ship or Mail Steamer
- M.V. for Motor Vessel
- R.M.M.V. for Royal Mail Motor Vessel
- T.S.S. for Twin-Screw / Triple Screw Propulsion Ship
You will often see documents from the same voyage using different designations such as S.S. "Steamship" and R.M.S. "Steamship."