Officer Candidate School 
Outer Continental Shelf 
Operational Control System 
Operational Control Segment 
Office of Coast Survey 
Office of Community Services 
Open Content Syndication 
Optical Control System 
Object Compatibility Standard 
Observatory Control System 
Onboard Checkout System 
Open Cabling System 
Obstacle Clearance Surface 
Occupational Course of Study 
Ocean Color Scanner 
Offensive Counter Space 
Offensive Counterspace 
Office of the Chief of Staff 
Office of the Chief Scientist 
Officers Candidate School 
Oklahoma Climatological Survey 
On-board Communications Station 
Onboard Computer System 
On-Card Sequencer 
Online Charging System 
Open Control System 
Operating Control System 
Operations and Control Software 
Optical Calibration Sphere 
Optical Control Subsystem