73 years ago a war photographer snapped the most iconic image of World War II — here's the story of the battle behind the photo

The objective of what was dubbed Operation Detachment was to capture the entire island, wiping out its defending garrison so that its three airfields and infrastructure could be used as a staging ground for attacks on the Japanese mainland.

American victory was never in doubt; the US had an overwhelming numerical advantage and complete aerial superiority and had cut off the island, preventing retreat or the arrival of reinforcements.

But the Japanese had prepared for a massive battle on the island. They had evacuated all civilians and burned all the vegetation and brush to eliminate places where the Americans could conceal themselves.

Most important, the Japanese had built a massive network of tunnels and bunkers that enabled them to access any part of the island and wait out long bombardments.

In the end, only 216 members of the garrison were taken prisoner. The rest of the troops died in combat or killed themselves — though an estimated 3,000 of them refused to surrender and continued to live in the island's massive underground fortifications, conducting raids and guerilla-style attacks.

The last Japanese soldiers to surrender on Iwo Jima did so on January 6, 1949, nearly four full years after the start of the battle and 3 1/2 years after the war ended.

Though Japanese combat deaths were three times as high as those of the US forces, total American casualties, which include dead and wounded, were higher than those of the Japanese — 6,821 Americans were killed, more than 19,000 were wounded, one escort carrier was sunk, and numerous other ships were damaged.

Check out some of the photos of the battle here:

Iwo Jima was strategically important, enough so that air and naval bombardments of the island started in June 1944, almost a year before the battle.

Iwo Jima's location provided Japanese fighters with a base to intercept US aircraft on their way to attack the Japanese mainland and had value as a staging area for the US. The Americans decided it had to be taken, and the first operations against Iwo Jima started as early June 1944.

But the island had been turned into a fortress by Lt. Gen. Tadamichi Kuribayashi. By the time the Americans invaded, Japanese soldiers had dug 11 miles of bunkers and tunnels all around the island.

Because the tunnels were so far underground, the Japanese could wait out any bombardments. One bunker was as far as 90 feet deep.

The US hit Iwo Jima with naval bombardments for three days. Though the explosions did knock out some trenches and caves, the effect was still limited because of the tunnels and bunkers.

The commander of the Marine landing force had originally requested 10 days of shelling, but the Navy cut it down to three.

Bad weather, combined with the Japanese tunnel and bunker networks, limited the damage that the barrages could do. Some American ships were even hit by return fire from the Japanese.

Up to 60,000 Marines and several thousand US Navy Seabees were to take part in the operation. "Victory was never in doubt. What was in doubt in all our minds was whether there would be any of us left to dedicate our cemetery at the end," Maj. Gen. Graves B. Erskine, who led the 3rd Marine Division, said of the battle.

The operation relied on small craft that would ferry troops and supplies to the island from the bigger ships and back again. They also had to carry back dead and wounded soldiers.

On February 19, 1945, the Marines landed.

The American high command knew the task would not be easy. Lt. Gen. Holland M. Smith, the commander of the reportedly said "this is going to be a rough one — we could suffer as many as 15,000 casualties here."

"It was an operation of one phase and one tactic ... until the mission was completed it was a matter of frontal assault maintained with relentless pressure," he said.

The Marines used multiple kinds of landing craft, like Higgins boats and Landing Vehicles Tracked (known as amphtracks or amtracs).

Once the Marines landed, they quickly found that the volcanic ash on the island was difficult to move in, got vehicles stuck, and slowed them down considerably.

The ash was softer than sand, and in some places slopes were as high as 15 feet. As a result, many tanks, amtracs, and other vehicles were stuck, and the Marines moved slower on the beaches.

All of this made the troops on the beach sitting ducks against Japanese artillery.

The Japanese had mortar and artillery positions all over the island. Mount Suribachi's high ground was a perfect area for spotters to call in artillery strikes on the Marines.

Additionally, since the Japanese had burned all vegetation — and because it was extremely difficult to dig foxholes in the ash — the Marines could not avoid being exposed.

They were essentially sitting ducks for artillery and the Japanese troops who were shooting at them from bunkers and trenches. The Time Life correspondent Robert Sherrod reported that "Iwo Jima can only be described as a nightmare in hell."

With constant bombardment, the Marines had no choice but to move forward. Taking Mount Suribachi became a primary objective.

As the Marines pushed further inland, Navy Seabees, Coast Guard sailors, and other troops began offloading weapons and supplies.

Navy Seabees, known officially as Naval Construction Battalions, are combat engineers. At Iwo Jima, they were tasked with building forward command posts, artillery positions, and field hospitals.

At the same time, they were expected to fight. The Navy had previously used civilian contractors for these jobs, but according to international law, civillian personnel who fight in wars are labeled as guerrillas, which means they can be executed, a loophole the Japanese used after they invaded Wake Island in 1941.

Combined with air and naval support, American artillery guns on the island allowed for quicker support that the Marines could call on.

Mount Suribachi was taken in the first week of the battle. It was here where Joe Rosenthal took his iconic photo of Marines raising the US flag.

While Mount Suribachi was tactically significant, the main Japanese defenses were not there but at the northeastern parts of the island, where the airfields were located.

Joe Rosenthal's famous photo was actually the second raising of a US flag over Mount Suribachi. The first flag was smaller and was replaced by the larger one that is in the photo after the secretary of the Navy, James Forrestal, decided he wanted the original flag as a

On the eastern side of the island, combat was still extremely intense. The airfields were well guarded, and Kuribayashi, the leader of the Japanese garrison, proved capable in defensive tactics.

Unlike in past battles, the Japanese troops on the island rarely conducted attacks. Kuribayashi had forbidden them, realizing that they were futile.

As a result, the Japanese were purely on the defensive, and they took their toll on the Americans."I don't know who he is, but the Japanese general running this show is one smart bastard," he said.

Capt. Dave Severence described the toll on his unit: "Easy Company started with 310 men. We suffered 75% casualties. Only 50 men boarded the ship after the battle. Seven officers went into battle with me. Only one — me — walked off Iwo."

The Marines used grenades and flamethrowers to force the Japanese out of their tunnels and bunkers. Japanese troops were occasionally offered a chance to surrender, but most were set on fighting to the death.

As the end of February came, the Japanese showed no sign of surrender or defeat. "Each man should think of his defense position as his graveyard, fight until the last, and inflict much damage to the enemy," Kuribayashi had said.

The tunnels and bunkers were proving hard to destroy.

Japanese resistance was still strong in early March, but progress was being made. By March 8, the Americans had managed to split the Japanese defenses on the island in two.

But resistance was still strong, mainly because of the tunnels and bunkers.

But American methods of forcing the Japanese out were taking their toll. The Japanese were also running low on food, water, and ammunition.

The Americans, on the other hand, were still getting supplies shipped in. Naval and air support was also proving to be very effective.

By mid-March, the Japanese troops were malnourished and holed up in horrible living conditions in bunkers and caves. The air and naval bombardments took their toll on the Japanese.

"I am not afraid of the fighting powers of only three American Marine Divisions if there are no bombardments from aircraft and warship. This is the only reason we have to see such miserable conditions," Kuribayashi reported.

Kuribayashi realized that the situation was hopeless. On the evening of March 23, he radioed his last message to Japan.

Though his body was never identified, Kuribayashi most likely died in a mass attack on American camps on the morning of March

Today, US and Japanese visitors to Iwo Jima, now allies, pay their respects to those who died in the battle. Here, American and Japanese veterans, US Marines and US Navy sailors, and others saluted in front of the Reunion of Honor Memorial on March 14, 1995, during a memorial service commemorating the 50th anniversary of the Battle of Iwo Jima.

The tradition of honoring the dead of the battle is still honored, as shown in this 2010 photo taken at the top of Mount Suribachi, where memorials to the US and Japanese troops are located.