SS — The Default Prefix The original civilian ship prefix is SS, which is an acronym for “steamship.” Back in the early days of powered water vessels, shipping companies wanted a way to distinguish their newer, faster steamships from older, slower sail and oar propelled watercraft.

Historically and in 2026 maritime tradition, SS stands for "Steamship" (or sometimes "Screw Steamer"). This prefix was popularized in the 19th century to distinguish modern vessels powered by steam engines from the older "SV" (Sailing Vessels). Specifically, "Screw Steamer" referred to ships using a submerged propeller (screw) rather than a paddle wheel. While most modern cruise ships and tankers are technically MV (Motor Vessel) because they use diesel engines, or MS (Motor Ship), the SS designation remains iconic due to famous liners like the SS United States or the SS Great Britain. In 2026, you may still see SS used for a handful of preserved heritage ships or specialized steam-turbine vessels. Understanding these prefixes is part of "ship-spotting" culture, where other common 2026 designations include GTS (Gas Turbine Ship) and NS (Nuclear Ship), though the latter is almost exclusively reserved for military vessels and icebreakers.