U-4

U-4 or U4 may refer to:

* German submarine "U-4", one of several German submarines
* U-4, the U.S. Air Force version of the Aero Commander (aircraft), a light twin-engined aircraft from Aero Design and Engineering Company
* U4, an unemployment figure released by the United States Bureau of Labor Statistics
* U4 spliceosomal RNA, a non-coding RNA component of the major U2-dependent spliceosome
* Anti-Corruption Resource Centre (U4), based at the Chr. Michelsen Institutein in Bergen, Norway
* U4 (Berlin U-Bahn), a subway line in Berlin, Germany
* U4 (Frankfurt U-Bahn), a subway line in Frankfurt, Germany
* London Buses route U4