The Marine Corps has opened an investigation into whether it misidentified one of the six men shown raising an American flag atop Mount Suribachi on Iwo Jima in February 1945, the Associated Press reported Monday. The picture, taken by AP photographer Joe Rosenthal, became one of the most enduring images of World War II, and the flag raisers’ identities have been accepted for decades.

In 2014, two amateur historians began raising issues regarding one service member supposedly depicted in the photo, Navy Corpsman John Bradley, according to the AP. Their evidence was first published in the Omaha World-Herald, and the paper was the first to report on the Marines’ new inquiry Saturday.

The picture, taken Feb. 23, 1945, actually depicted the raising of the second flag that day. The first was quickly raised, taken down and replaced with the second, larger one. The second flag, taken off a nearby landing ship, was raised by five Marines and one Navy corpsman. The battle for the island was still underway, and the Marines had made it a point to take the mountain on which the flag was raised. The 550-foot-high mound of volcanic earth was an important piece of terrain that overlooked the small pork-chop-shaped island.

The battle for Iwo Jima, known as Operation Detachment, would claim the lives of more than 5,000 Marines and almost 18,000 Japanese soldiers in little more than a month. The island was deemed an essential objective of the Allied war effort, as it had a lone airstrip that could be used as a landing site for American B-29 bombers returning from air raids over Japan. The battle was brutal, and the Japanese defenders almost all fought to the death, holding out for 36 days entrenched in an extensive network of tunnels and caves.

“The Marine Corps is examining information provided by a private organization related [to] Joe Rosenthal’s Associated Press photograph of the second flag raising on Iwo Jima,” Marine Corps spokesman Maj. Chris Devine said in an emailed statement.

Devine did not give a timeline for the investigation.

“Rosenthal’s photo captured a single moment in the 36-day battle during which more than 6,500 U.S. servicemen made the ultimate sacrifice for our Nation, and it is representative of the more than 70,000 U.S. Marines, Sailors, Soldiers and Coast Guardsmen that took part in the battle. We are humbled by the service and sacrifice of all who fought on Iwo Jima,” Devine added.

The Marines, at the time, identified the men depicted in Rosenthal’s photo as John Bradley, Rene Gagnon, Ira Hayes, Harlon Block, Michael Strank and Franklin Sousley. Rosenthal did not immediately get the names of the flag raisers, and only after the photograph received widespread attention did the Marines set out to find the men in the photograph.

There was some initial confusion in the months after the battle about whether Block was in the photo, and Rosenthal came under fire for supposedly staging the photo after he mistakenly admitted to doing so when someone had inquired about what he thought was a different picture.

Over the course of the battle, Block, Strank and Sousley were all killed in the fighting. Bradley, Gagnon and Hayes would return home to sell war bonds while the remainder of their unit — the 5th Marine Division — shipped back to Hawaii.

The two historians, Eric Krelle and Stephen Foley, have put forth evidence that calls into question Bradley’s participation in the photo, according to the AP. The discrepancies mostly revolve around Bradley’s job as a corpsman, which is the Navy’s term for combat medic.

According to the two, and reported by the AP, Bradley is wearing a cartridge belt designed to hold rifle magazines and has wire cutters hanging from one of his pockets. As a corpsman, he would likely not have had a rifle and would have had no need for wire cutters. Corpsmen, in World War II, were mostly armed with only a pistol so that their hands were free to work on patients. The historians also point out issues with Bradley’s pants and the presence of a hat underneath his helmet in the photo. According to the AP report, Bradley’s pants are not cuffed in the photo, but other pictures from that day show his pants cuffed. Also, in other photos from the day, he is not wearing a hat under his helmet, according to the report.

Bradley’s son, James Bradley, wrote a book about his father and the flag raisers in the book “Flags of our Fathers.” The book was turned into a movie by the same name and directed by Clint Eastwood. Bradley conducted extensive research into the book and was shocked when contacted by the AP regarding the recent investigation. His father, a recipient of the Navy Cross for heroism during the battle, died in 1994.

“This is unbelievable,” Bradley told the AP. “I’m interested in facts and truths, so that’s fine, but I don’t know what’s happening.”

An earlier version of this post said the 5th Marine Division left Iwo Jima and headed to Okinawa, when in fact the division returned to Hawaii. 

Read more: