OGA is short for Other Government Agency, which is usually the Central Intelligence Agency or the National Security Agency, or CIA and NSA for short. The CIA is responsible for Human Intelligence, while NSA domain is Signals Intelligence, or interception of communications sent by technology.
Indig is short for Indigenous.
RECCE is short for Reconnaissance.
Tango either refers to Target or the letter T in the phonetic alphabet.
Infil is short for Infiltration.