Iwo Jima is an island located near Japan and during World War 2 it was being used by the Japanese as an air base. The United States deemed it necessary to capture this island since it would allow them to conduct bombing runs on Japan's mainland, which wasn't possible using their other air bases. The Japanese knew that if they lost Iwo Jima, they would be put in a very vulnerable position from the air and sea.
In June of 1944, the United States started bombing runs from its aircraft carriers in the area. Over ten days, the island was bombarded from the air and sea, making it the victim of the most intensive bombing on any Pacific island during World War 2.
On February 19th, 1945, marines from the 4th and 5th divisions landed on the beaches and moved in, finding surprisingly little resistance. Once naval bombardment was ceased to allow the marines to move in further, Japanese forces poured from underground bunkers to defend their position. Despite this heavy resistance, the marines were able to push forward and seize a waypoint known as "The Quarry".
The next day, more marines landed at the south end of the island and moved forward to seize Mount Suribachi. Other forces managed to take one of the airfields and by the end of the day, over a third of the island was under US control. It required an additional three days for marine forces to reach the summit of Mount Suribachi and raise their flag.
As more marines landed on the island, Lieutenant General Tadamishi Kuribayashi, the Japanese commander, decided to retract his forces to defend the central and northern portions of the island. Japanese forces hid in the extensive underground bunker networks, providing high resistance to the advance of the marines. Despite these concentrated defenses, marines from the 3rd division were able to move northeast and seize a second airfield on March 9th. As the 5th division simultaneously moved along the western coast, the desperate Japanese forces launched a banzai attack, resulting in 700 casualties on their side.
Now that the US forces controlled the majority of the island and its airfields, aircraft were able to make emergency landings for refueling and repairs after making bombing runs. The first such landing occurred on March 4th and the B29 bomber was able to get repaired and take off to return to its air base. By mid-March, Japanese resistance was confined to the northern tip of the island and marines moved quickly, destroying small groups of soldiers one-by-one.
On March 26th, the island was declared secure and all Japanese forces were either captured or killed. On April 4th, the 147th regiment of the army took control of the island, allowing the marines to continue their campaign.
The battle was a success for the United States, but in the process nearly 7,000 soldiers were killed and another 19,000 were wounded. Only 1,083 of the approximately 20,000 Japanese soldiers managed to survive the battle. The loss of life was not in vain, however, since over 2,000 bombing aircraft were able to make emergency landings on the island rather than crash and burn. The seizure of Iwo Jima was yet another nail in Japan's coffin, eventually causing them to surrender.