3U or 3-U may refer to: Sichuan Airlines's IATA code A type of Rack unit Zerstörergeschwader 26, from its historic Geschwaderkennung code with the Luftwaffe in World War II A CubeSat measuring 30×10×10 cm The acronym for the third (3rd) catalog of Uhuru x-ray sources See also U3 (disambiguation)