sandbags piled up in a trench dug in the ground to protect soldiers and slits to look out and shoot from

bags barricade communication trench conflict defence defend defense dig digging ditch dugout entrench entrenchment excavating excavation first world war foxhole great guard hessian hole jute loophole military protect sack sacking sand sandbag sandbags shelter slit slot soldierly trenches trenching warfare watch dug ground army soldiers enemy raids fortification strategy battlefield