U-1, the USAF and US Military's designation for the De Havilland Canada DHC-3 Otter light transport aircraft U-1, Soviet designation for Avro 504 trainer. Multiple German U-Boats named U-1 Oberursel U.I, an early German aircraft engine HDMS U-1, a Danish submarine SM U-1, an Austro-Hungarian submarine, lead ship of the U-1 class