During World War II, allied field hospitals were mobile. They usually held about 400 beds while the more stationary evacuation hospitals could be 400 or 750 bed hospitals. The mobile hospitals would arrive within days after an invasion and would move with the armies, always remaining a few miles behind the front lines. They usually used canvas tents but would also use any buildings in the area when available. When the field hospital was about to move, they stopped accepting casualties and sent those they had to other field hospitals. They then packed their tents and equipment onto trucks and moved to the new location. Within a few hours they were ready to accept wounded soldiers again.