O ~ Observer

OBE ~ Officer of the British Empire

OBLI ~ Oxfordshire & Buckinghamshire Light Infantry

OBOS ~ Overseas Branch Ordnance Survey

OC ~ Officer Cadet

OC ~ Officer Commanding

OC & E ~ Officer's Clothing & Equipment

OCROD ~ Officer Commanding Railway Operating Division

OF ~ Ordnance Factory

Offr ~ Officer

OHMS ~ On His Majesty's Service

Oi/c ~ Officer-in-Charge

OIR ~ l'Office Reconstitution Industrielle (post-war disposals)

OLI ~ Oxfordshire Light Infantry

OM ~ Member of the Order of Merit

OMR ~ Official Municiple Receiver

OMW ~ Ordnance Mobile Workshop

OO ~ Ordnance Officer

OP ~ Observation Post

OR ~ Other Rank

OR ~ Ontario Regiment (Canada)

orbat ~ Order of Battle

Ord ~ Ordnance

ORS ~ Orderly Room Sergeant

OS ~ Ordnance Survey

OTC ~ Officer Training Corps