Seventy-five years ago today, six United States Marines raised the American flag atop Mount Suribachi during the Battle of Iwo Jima, near the end of World War II.

This classic Associated Press photo by Joe Rosenthal is the only photo ever to win the Pulitzer Prize the same year it was taken. Rosenthal denied charges it was "staged" until his death in 2006. The photo was used as the basis for the Marine Corps War Memorial in Washington, D.C., completed in 1954.

U.S. Marines of the 28th Regiment, 5th Division, raise the American flag atop Mt. Suribachi, Iwo Jima, on Feb. 23, 1945. AP Photo/Joe Rosenthal

The Battle of Iwo Jima

Iwo Jima, one of the Bonin Islands, located about 750 miles south of the Japanese mainland, featured a strategic military installation with three airfields. There were approximately 21,000 Japanese soldiers on the island.

The Americans had taken control of bases in the Mariana and Marshall Islands, and were conducting raids upon Japan, from nearly twice the distance as Iwo Jima, which also served as an early-warning outpost for the mainland, and a launching pad for attacks upon U.S. facilities.

The Marine invasion, dubbed Operation Detachment, was aimed at securing the island as a refueling area for U.S. planes. The battle itself followed several months of American bombing raids and bombardment from ships.

The first invasion forces, which landed on the island on February 19, included 74,000 Marines, Navy Seabees, Army and Coast Guard. The very ground of the island – volcanic ash – was precipitous to the invaders, and as they started to advance, the Japanese, heavily dug into a vast system of bunkers and tunnels, opened fire.

Though a portion of the beach was secured, losses were extremely heavy. Frank Matthews, then an 18-year-old private, was part of a team providing relief for a 900-man regiment, the 25th Marines' 3rd Battalion, which was practically wiped out on the very first day of fighting.

"They lost 750 in one five-hour stretch," Matthews told CBS News' David Martin in 2015. "Every inch of that beach and everything around it had been pinned down and zeroed in by the Japanese guns."

Lawrence Snowden was a 23-year-old Marine captain: "When we landed, there were three colors: black and gray, from all the exploding ordinance; the third color was red – blood," he told Martin.

The fighting would last more than a month, becoming one of the bloodiest battles of the Pacific War.

Japanese soldiers would engage in charges, often in darkness, or would ambush Americans from their tunnels. As the Japanese forces' supplies ran out, some surrendered, but only about two hundred were taken prisoner. The remainder were killed in action or committed suicide.

By the time the battle ended on March 26, nearly 7,000 Americans had died, and 20,000 more had been injured. Total U.S. casualties were greater than those of the Japanese – the only Marine Corps battle in the war where that was the case.

The island, with its maze of tunnels and large amount of unexploded ordnance, was largely unused after the war. About 12,000 Japanese, and nearly 200 Americans, are still classified as missing, presumed killed. Remains continue to be recovered.

In 2018 it was announced that ground-penetrating radar would be used to help locate remains.