O5

O5 or O-5 may refer to:

The Outreach Five a.k.a "Group of Five", emerging economies in the G8+5 forum: China, Mexico, India, Brazil and South Africa
A symbol for the anti-Nazi Austrian Resistance, where the 5 stands for E and OE is the abbreviation of Österreich
USS O-5 (SS-66), a 1917 O-class submarine
HNLMS O 5, a 1913 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
LNER sub-class O4/5, 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 Army, Marine Corps, Air Force, and Space Force
- Commander in the Navy, Coast Guard, Public Health Service Commissioned Corps, and NOAA Commissioned Officer Corps
Otoyol 5, a toll motorway in Turkey
The time-displaced X-Men, also called "The Original 5"
The senior “overseer” position in the fictional SCP Foundation

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