The terrain on Iwo Jima was well-suited to the defense and provided the Japanese with a significant ability to slow and impede the American Marines. The initial plan called for a campaign of not more than four days and it ended up taking 36, and that does not count the mop-up operations of Army units for basically two months in April and May of 1945. The Japanese delayed and slowed the American advance at every opportunity and made skillful use of terrain to build and fortify their positions. The evidence of the casualty statistics. The Vth Amphibious Corps had an assigned strength of 71,245 troops, and suffered 25,851 casualties.H.Schubert wrote:Thanks for the input Landser,
IwoJima was not a dream position to defend, but there have been worse, especially in early battles against china before the Shanghai battle.
The terrain on Iwojima gave not many favorable positions to allow the defender, to target a large section of flat terrain, allowing machine gun fire to repell a hudge number of attackers with only one or few machine gun positions. The beaches offered the best and unique chance to basicly shoot a will at any approaching boat .
The main problem for these positions would have been to shield them from massive bombardements, before the actual landing of the attackers on the beaches. There was no effective measure (or precise) measure for destroyers or airplanes to bombard close beach machine gun positions, after forces have landed on that beach section, do to the difficluty of precision bombing.
The topography of the island favored the defender, with little in the way of natural concealment, no hard-surfaced roads, a commanding volcano with a height of nearly 450 feet, etc. The northern half of the island, named the Motoyama Plateau, was a jumbled wasteland of volcanic slag, with countless tiny arroyos, ridges and draws, many of which had no improved paths for vehicular access. The Japanese dug down into the island, created miles of tunnels, bunkers, emplacements, many of which were protected from indirect fire, and hidden from American reconnaissance until the moment when the Marines approached at close range.
During the assault landing on D-Day, the Japanese defenders pounded the beach head with indirect fire, this after days of preparatory bombardment from the Navy and multiple air raids by US bombers. There were literally thousands of Japanese positions, so many in fact, that there was not enough ammunition to destroy them all.
The Japanese knew they could not achieve a comprehensive victory on Iwo Jima. The story of the island's commander has been well-documented and he seems to have been a good officer and a sympathetic character. But his concept of operations was to slow and delay the Americans for as long as possible, effectively making the Marines bleed for every yard of ground. In January 1945 General Kuribayashi adopted a defensive concept abandoning the idea of strong beach defenses and the traditional Japanese banzai counter-attacks. Instead, he specified well-sited, prepared defensive positions with multiple interlocked fields of fire, hidden artillery emplacement, and stockpiled supplies for prolonged defense.
The map below shows the VAC landing plan with the objective lines for the operations. The color image is from Marine combat camera film and shows prep fires on an objective during the battle for Iwo Jima. Marine commanders expected a fight similar to Saipan in terms of the Japanese response to the landing with the Japanese coming out in banzai attacks to break their own backs, so to speak. This never happened (except in a small example too late in the battle to matter in the larger sense,) and instead of the projected 3 to 4 days, the campaign took 36. A great deal of the indirect fire that was shot in support of the Marines had little or no affect on the Japanese, since the volcanic ground absorbed the impacts so well, and the Japanese had dug down so well and deep.