Calque ofGermanU-Boot.

U-boat (pluralU-boats)

1. (military,nautical,historical) AnyGermansubmarine of theFirst orSecond World War, or anyAustro-Hungarian submarine of the First World War.
2. (shipping) A narrow utility cart with tall handles on both ends that is used to carry loads of retail products to be sold, so named because its shape is roughly that of a capitalU.
3. (rail transport,slang) Nickname given to theGeneral Electric Universal Series diesel-electric locomotives.

• Touba,Tuoba,about