Battle of Iwo Jima
The first flag on Iwo Jima: On Feb. 19, 1945, the 4th and 5th Marine Divisions stormed ashore on Iwo Jima. The battle continued with the Japanese into March during the Pacific Campaign of World War II. The U.S. invasion, known as Operation Detachment, was charged with the mission of capturing the airfields on Iwo Jima.

The battle was marked by some of the fiercest fighting of the campaign. The Imperial Japanese Army positions on the island were heavily fortified, with vast bunkers, hidden artillery, and 18 kilometers (11 mi) of tunnels. he battle was the first American attack on the Japanese Home Islands and the Imperial soldiers defended their positions tenaciously. Of the 21,000 Japanese soldiers present at the beginning of the battle, over 20,000 were killed and only 216 taken prisoner.

Joe Rosenthal photographed five Marines and a U.S. Navy corpsman raising the U.S. flag atop the 166 meter (546 ft) Mount Suribachi. The photograph records what was actually the second flag-raising on the mountain, which took place on the fifth day of the 35-day battle. The picture became the iconic image of the battle and may be the most reproduced photograph of all time.

Geography
Iwo Jima is a volcanic island about 1,200 km (650 nautical miles) south of Tokyo, 1,300 km (702 nautical miles) north of Guam and approximately halfway between Tokyo and Saipan (24.756°N, 141.290°E). It is approximately 21 square kilometers (5,200 ac), with Mount Suribachi at its southern tip being its most prominent feature. In June 2007 the island was officially renamed Iwo To, a name that had been used by local residents before the war. The name was changed on protest from former residents and after two popular Clint Eastwood films (Flags of Our Fathers and Letters From Iwo Jima) eferenced the island as Iwo Jima. The Japanese characters for Iwo Jima and Iwo To are the same, but the pronunciation changed when Japanese soldiers arrived and pronounced it differently than the residents.

Background
After the American seizure of the Marshall Islands and devastating air attacks against Truk in the Caroline Islands in February 1944 the Japanese military leadership reappraised the military situation. All indications pointed to an American drive towards the Marianas and Carolines. To counter such a move they established an inner line of defense extending generally northward from the Carolines to the Marianas, and thence to the Ogasawara Islands. In March 1944 the Thirty-First Army, commanded by General Hideyoshi Obata, was activated for the purpose of garrisoning this inner line. The commander of the Chichi Jima garrison was placed nominally in command of Army and Navy units in the Ogasawara Islands.

Following the American seizure of bases in the Marshalls in the battles of Kwajalein and Eniwetok in February 1944 both Army and Navy reinforcements were sent to Iwo Jima. Five hundred men from the naval base at Yokosuka and an additional 500 from Chichi Jima reached Iwo Jima during March and April 1944. At the same time, with the arrival of reinforcements from Chichi Jima and the home islands, the Army garrison on Iwo Jima had reached a strength of over 5,000 men, equipped with 13 artillery pieces, 200 light and heavy machine guns, and 4,552 rifles. In addition there were numerous 120 mm coastal artillery guns, twelve heavy anti-aircraft guns, and thirty 25 mm dual-mount anti-aircraft guns.

The loss of the Marianas during the northern summer of 1944 greatly increased the importance of the Ogasawaras for the Japanese, who were well aware that the loss of these islands would facilitate American air raids against the home islands, disrupting war manufacturing and severely damaging civilian morale.

Final Japanese plans for the defense of the Ogasawaras were overshadowed by the fact that the Imperial Japanese Navy had already lost most of its strength and could no longer prevent American landings. Moreover, aircraft losses throughout 1944 had been so heavy that, even if war production were not affected by American air attacks, combined Japanese air strength was not expected to increase to 3,000 aircraft until March or April 1945. Even then, these planes could not be used from bases in the home islands against Iwo Jima because their range did not exceed 900 km (559 miles); besides, all available aircraft had to be hoarded for possible use on Taiwan and adjacent islands near land bases.

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In a postwar study, Japanese staff officers described the strategy applied in the defense of Iwo Jima in the following terms:

In the light of the above situation, seeing that it was impossible to conduct our air, sea, and ground operations on Iwo Jima toward ultimate victory, it was decided that in order to gain time necessary for the preparation of the Homeland defence, our forces should rely solely upon the established defensive equipment in that area, checking the enemy by delaying tactics. Even the suicidal attacks by small groups of our Army and Navy airplanes, the surprise attacks by our submarines, and the actions of parachute units, although effective, could be regarded only as a strategical ruse on our part. It was a most depressing thought that we had no available means left for the exploitation of the strategical opportunities which might from time to time occur in the course of these operations.

Daily bomber raids from the Marianas hit the mainland as part of Operation Scavenger. Iwo Jima served as an early warning station which radioed reports of incoming bombers back to mainland Japan, allowing Japanese air defenses to be prepared for the arrival of American bombers.

At the end of the Battle of Leyte in the Philippines the Allies were left with a two month lull in their operations prior to the planned invasion of Okinawa. Iwo Jima was strategically important: it provided an airbase for Japanese aircraft to intercept long-range B-29 bombers and provided a haven for Japanese naval units in dire need of any support available. The capture of Iwo Jima would eliminate these problems and provide a staging area for the eventual invasion of the Japanese mainland. The distance of B-29 raids would be nearly halved, and a base would be available for P-51 Mustang fighters to escort and protect the devastating bomber raids. Intelligence sources were confident that Iwo Jima would fall in five days, unaware that the Japanese were preparing a quintessentially defensive posture, radically departing from any of their previous tactics. So successful was the Japanese preparation that it was discovered after the battle that the hundreds of tons of Allied bombs and thousands of rounds of heavy naval gunfire left the Japanese defenders almost unscathed and ready to wreak losses on the U.S. Marines unparalleled up to that point in the Pacific War. In the light of the optimistic intelligence reports, the decision was made to invade Iwo Jima: the landing was designated Operation Detachment.