U1

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

Arts and entertainment

 * Ultima I: The First Age of Darkness, a 1981 video game
 * Yuvan Shankar Raja (stage name: U1; born 1979), a Tamil musician and film composer
 * U1 Technology, a video game publisher
 * U-1, protagonist of the Gitaroo Man video game

Computing and mathematics

 * U(1), in abstract algebra, the unitary group of degree one
 * U1, a speed class for Secure Digital (SD) cards
 * Apple U1, a mobile system-on-a-chip

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

Locomotives

 * LNER Class U1, a 1924 British solitary loco
 * SR U1 class, a class of 2-6-0 locos

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)

Other uses

 * 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