back line defense

back-to-back circuit

back-to-back connection

back-to-back radio stations

back-to-back relay

deployment line; line of deployment (LD); line of departure

fall back to a new line

perimeter defense (all-around defense)

beach defense mine / beach-defense mine

main defense area (line) / main defensive position

main line of defense (resistance)

outline the main line of defense (of the enemy)

main defense (line) area

observer-target line (OT line)

scheme trail line (tag line)

back-up fire control

back-up system

cut back co-operation

I read back

play back kit

pull back

push back

read back

reverse engineering ( back- wards engineering)

Camel-back water pouch

Field Pack, Air Support Back

back brief / backbrief

peel back

back on the block

back-up circuit breaker

armor back plate

back bearing housing

back blow