By the third day after landing on Peleliu, the First Marine Division had overwhelmed the Japanese beach defenses and taken control of the airfield they had been sent to seize. But from cave emplacements overlooking the airfield, on a series of limestone hills and coral ridges known as the Umurbrogol, the enemy poured down fire on the Marines. No prior intelligence had prepared the Marines for this.
"Most of the Japanese defenders were entrenched in those ugly hills," says historian Donald L. Miller, author of 'D-Days in the Pacific' and a consultant on HBO's miniseries. "All of the Marines' training had been directed toward storming the beaches and taking the airfield, but now they found that the airfield was almost useless if they didn't gain control of the high ground above it. The Japanese were firing on American planes as they took off and landed. To secure the airfield, the First Division had to go up and take those hills."
"The Japanese would rely on a defense-in-depth strategy, luring the Americans toward their strong points and unleashing hurricanes of fire."
But the enemy's ingeniously designed system of interlocking defenses slowed the Marines to a crawl. The men would advance on an enemy gun pit, only to take fire on their rear from a cave high above them. This claustrophobic battlefield negated the Americans' greatest strength: heavy weapons like tanks, artillery, and aircraft. The men paid dearly for every scrap of territory they gained, as the Japanese attacked from positions of cover and then retreated deep into their caves. The three-to-four day battle that Marine commanders had anticipated lasted into November, as Marines, and later elements of the Army's 81st Division, slowly rooted out the Japanese until nearly every defender was dead.
"Beginning with Peleliu," says Miller, "the Japanese would rely on a defense-in-depth strategy, luring the Americans toward their strong points and unleashing hurricanes of fire from positions that neither naval nor air bombardment could reach. Japan couldn't win the war this way, but it could hope to make it so damn costly that the American public would demand an end to the bloodshed without insisting on unconditional surrender. That, at least, was what the Japanese hoped would happen."
After a brief rest back on the island of Pavuvu, the veterans of Peleliu would again confront this defense-in-depth strategy. Only on Okinawa, their next destination, they would face a vastly larger defensive force.