U 23
U 23 stands for:
- an age group in sport, see class division in sport #Age classes
- U 23 - Deadly Depths , American war film from 1958
- alternative designation of the Citroën type 23
U 23 denotes several submarines:
- SM U 23 (1913–1915), submarine of the German Imperial Navy
- U 23 (kuk Marine) (1916–1918), submarine of the Austro-Hungarian Navy
- U 23 (Kriegsmarine) (1936–1944), submarine of the German Kriegsmarine
- U 23 (Bundeswehr) (1975–2011), submarine of the German Navy
