Terms:

objective
objective force level
obligated reservist
oblique air photograph strip
obliquity
observer-target range
obstacle
obstacle belt
obstacle clearing
obstacle intelligence
obstacle restricted areas
obstacle zone
occupational and environmental health surveillance
occupational and environmental health threats
occupied territory
Ocean Cargo Clearance Authority
oceanography
offensive counterair
offensive counterair attack operations
offensive minefield
offensive space control
office
officer in tactical command
officer of the deck
official information
off-load preparation party
offset costs
offset distance (nuclear)
offset lasing
offshore assets
offshore bulk fuel system
offshore petroleum discharge system
off-the-shelf item
on berth
on-call
on-call resupply
on-call target
on-call target (nuclear)
on hand
on-scene commander
on-station time
open improved storage space
open ocean
open-source intelligence
open unimproved wet space
operating forces
operating level of supply
operation
operational architecture
operational area
operational art
operational authority
operational characteristics
operational contract support
operational control
operational design
operational design element
operational documentation
operational environment
operational evaluation
operational exposure guide
operational intelligence
operational level of war
operational limitation
operationally ready
operational necessity
operational pause
operational reach
Operational Requirements Document
operational reserve
operational support airlift
operational testing
operation and maintenance
operation annexes
operation map
operation order
operation plan
operations center
operations research
operations security
operations security indicators
operations security measures
operations security planning guidance
operations security vulnerability
operations support element
operations to restore order
opportune lift
opportunity target
opposite numbers
orbital injection
orbit determination
order and shipping time
ordered departure
order time
ordnance
organic
organizational equipment
organizational maintenance
organization for combat
organization for embarkation
organization for landing
Organized Crime Drug Enforcement Task Force
origin
original negative
original positive
originator
other detainee
other government agency
other war reserve materiel requirement
other war reserve materiel requirement, balance
other war reserve materiel requirement, protectable
other war reserve stock
outbound traffic
outer fix
outer landing ship areas
outer transport area
outsized cargo
overhaul
overhead clearance
overlap
overlay
overseas
Overseas Environmental Baseline Guidance Document
overseas search and rescue region
oversized cargo
over the beach operations
over-the-horizon amphibious operations
over-the-horizon radar
overt operation
overt peacetime psychological operations programs