observation slit

observation point / observation post (OP)

slit trench

slit type of sight

vision slit

narrow slit trench

weapon slit

view slit

shell slit

fire slit

slit one's throat

sight slit

sighting slit

close observation

command-and-observation post

forward observer (FO), forward observation officer; (artillery) observer / spotter

hostile observation

infrared night vision observation device

observation aircraft (O; obsn acft)

observation facilities

observation flight

observation patrol

observation satellite

supervise the observation of armistice conditions

type of observation

United Nations India-Pakistan Observation Mission (UNIPOM)

United Nations Iraq-Kuwait Observation Mission (UNIKOM)

United Nations Observation Group in Lebanon (UNOGIL)

United Nations Yemen Observation Mission (UNYOM)

SLOCTOP (security, location, communication, targeting, observation, and position improvement)

artillery observation post

bilateral observation

bilateral observation point