According to postwar studies, the Imperial Japanese Navy was already unable to defend the empire's island holdings, including the Marshall Archipelago, due to its severe depletion from earlier Pacific War conflicts. The Japanese air force had also lost many of its jets, so the remaining ones couldn't defend the empire's military's "inner line of defense." Iwo Jima was one of the islands in this chain of defense. Armed forces officials in the United States used this intelligence to plot a few-day assault on the island. Iwo Jima's rugged terrain and dense forests provided the Japanese with ideal cover for their newly developed defensive strategy. Despite heavy aerial bombing and heavy gunfire from ships off the coast of Iwo Jima by Allied forces led by the Americans, the forces controlling the island suffered relatively little damage thanks to a strategy developed by Japanese General Tadamichi Kuribayashi. They were thus prepared to repel the initial attack by U.S. Marines under the command of Holland M. "Howlin' Mad" Smith.

When U.S. Marines landed on Iwo Jima via amphibious landing on February 19, 1945, they were immediately confronted with unexpected obstacles. The island's beaches were primarily composed of steep dunes of soft, gray volcanic ash, making it difficult to acquire a firm footing and navigate the area with cars. The Japanese waited in ambush as the Marines fought their way forward. The Americans believed their pre-attack bombing had successfully weakened the island's fortifications. However, Kuribayashi's strategy all along included a delay in reaction. When the American Marines were having trouble getting a foothold on the beaches of Iwo Jima, Kuribayashi ordered his artillery positions in the mountains above to commence fire, slowing their advance and killing many of them. The Marines were able to advance past the shore and secure a portion of one of Iwo Jima's airfields, fulfilling the invasion's stated objective, despite a banzai charge by scores of Japanese forces as twilight set.

Over the course of a few days, over 70,000 Marines from the United States arrived on Iwo Jima. Many Americans were hurt or killed during the five weeks of warfare, with some estimates putting the total at over 25,000 injuries, including approximately 7,000 deaths. This was despite the fact that the Americans outnumbered the Japanese on the island by more than three to one. The Japanese, however, had also sustained heavy casualties and were beginning to experience shortages of both food and weaponry. Under Kuribayashi's command, the majority of their defenses were carried out during the night. While the Japanese military was successful, it felt like their efforts were only delaying the inevitable. On day four of the battle, U.S. Marines captured Mount Suribachi on Iwo Jima's southern slope. An American flag was memorably raised atop the mountain. Joe Rosenthal, a photographer for the Associated Press, captured the picture and later won a Pulitzer Prize for it. The war, however, was far from over.

For four weeks, Kuribayashi virtually established a stronghold in the mountains of northern Iwo Jima as fierce fighting raged below. Three hundred of Kuribayashi's troops launched their final banzai on March 25, 1945. Although the American soldiers suffered heavy losses, they were able to successfully halt the assault. The United States claimed victory on Iwo Jima the following day, although it actually spent weeks searching the island's jungles for and eliminating Japanese "holdouts" who refused to surrender and continued fighting. During this procedure, many Americans lost their lives. For almost four years after the end of World War II, two Japanese holdouts remained hidden in the island's caverns, surviving off of scavenged food and supplies until they finally surrendered in 1949. Neither the U.S. Army nor the U.S. Navy were able to successfully utilize Iwo Jima as a base of operations during World War II. The airfields used by Air Force pilots for emergency landings were rebuilt by Navy Seabees, or construction battalions.