U1, U.I or U-1 may refer to:

Mathematics

*U(1), the degree one '' unitary group''

Military

*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

Entertainment

U1 Technology ''Little Fighter Online'' (LFO, Chinese: 小朋友齊打交 Online) was a fighting game for Microsoft Windows. It was popular at launch in Hong Kong, but has shown a rapid decline in popularity since. The gameplay itself was based on the earlie ...

, a game and software developing company *'' Ultima I: The First Age of Darkness'', a 1981 video game

People

* U1, alias for Yuvan Shankar Raja (born 1979), a Tamil musician and film composer *U-1, the main character in the video game '' Gitaroo Man'' for the PlayStation 2/PlayStation Portable

Railways

LNER Class U1 The London and North Eastern Railway Class U1 was a solitary Beyer-Garratt locomotive designed for banking coal trains over the Worsborough Bank, a steeply graded line in South Yorkshire and part of the Woodhead Route. It was both the longest ...

, a 1924 British solitary 2-8-0+0-8-2 Beyer-Garratt locomotive * SR U1 class, a class of 2-6-0 locomotives developed from the U Class

U-Bahn lines

* U1 (Berlin U-Bahn) * U1 (Frankfurt U-Bahn) * U1 (Hamburg U-Bahn) * U1 (Munich U-Bahn) * U1 (Nuremberg U-Bahn) * U1 (Vienna U-Bahn)

Technology

* Secure Digital (SD) Cards, class of speed * Apple U1

Other

*U1, unemployment figure released by Bureau of Labor Statistics * U1 spliceosomal RNA, a small nuclear RNA component of the spliceosome involved in pre-mRNA splicing.