O5

O5 may refer to:

• The "Outreach 5" emerging economies: China, Mexico, India, Brazil and South Africa. See Heiligendamm Process.
• USS O-5 (SS-66), an O-class submarine
• HNLMS O 5 a O 2 class submarine of the Royal Netherlands Navy
• SM UC-99, a U-boat renamed O-5 for Japanese service from 1920 to 1921
• Douglas World Cruiser, also designated as Douglas O-5
• De Havilland Canada Dash 7, also designated as De Havilland Canada O-5
• a subclass of the LNER Class O4 locomotive class
• O-5, the pay grade for the following officer ranks in the U.S. uniformed services: lieutenant colonel in the U.S. Army, U.S. Air Force, and U.S. Marine Corps; commander in the U.S. Navy, U.S. Coast Guard, U.S. Public Health Service Commissioned Corps, and NOAA Commissioned Officer Corps