 Cave entrances were opened or altered to be slanted as a defense against grenade and flamethrower attacks.The caves and bunkers were connected to a vast tunnel and trench system throughout central Peleliu, which allowed the Japanese to evacuate or reoccupy positions as needed, and to take advantage of shrinking interior lines.The Japanese were well armed with and mortars and anti-aircraft cannons, backed by a light tank unit and an anti-aircraft detachment.