 For two weeks, U.S. infantry, ably supported by Marine aviation and naval gunfire together with the Philippine Commonwealth Army forces, fought the Japanese along a five-mile (8 km) front, in terrain so rugged that tanks could not be used, and in positions heavily fortified with deep earthen emplacements, barbed wire, minefields, and booby traps.On 23 March, after heavy fighting, the center of the Japanese line finally broke, and in the next three days, the 162nd Infantry continued eliminating resistance in the central sector.The 186th Infantry, replacing the 163rd, continued the attack and the 54th Japanese IMB was forced to pull out a week later, harried by the Philippine Commonwealth troops & guerrilla units, retreating through the peninsula and into the jungle.