A deep moat had been dug around the castle.
They dug a trench to prevent the enemy from invading.
air-raid shelter; dugout
Only when written 壕
Specifically an underground shelter used during air raids. Written only with 壕.
During the war, people took shelter in air-raid shelters.
The soldiers dug a trench during the night.
When the air-raid siren sounded, people ran into the shelter.
The soldier hid in the trench to avoid the enemy's attack.
cover trench; shelter trench
bomb shelter; dugout; trench