The longest continuous battle of World War II went on for nearly six years, but its legacy is often overshadowed by better-known clashes in the European and Pacific Theatres. Nevertheless, the Battle of the Atlantic ranks amongst naval history’s “largest and most complex” campaigns: As Michael E. Ruane writes for The Washington Post, an estimated 90 ships, including four German U-boats, sank off of the North Carolina coast between January and July 1942.

One of these doomed submarines—U-576, piloted by 29-year-old captain-lieutenant Hans-Dieter Heinicke—was rediscovered in 2014 some 72 years after its July 15, 1942, sinking. It remained unexplored until 2016, when researchers from the National Oceanic and Atmospheric Administration (NOAA) began work on the wreck. Now, Ruane reports in a separate article for The Washington Post, these scientists have finally revealed the results of an advanced laser scan completed during the 2016 probe, offering what senior NOAA archaeologist Joe Hoyt describes as “the clearest picture I’ve seen of any U-boat on the seabed.”

The survey also offers key clues regarding U-576’s final moments. As Ruane explains, the vessel appears to be fully intact, suggesting it wasn’t the victim of an uncontrolled sinking. Instead, the evidence points to mechanical issues that may have prevented the sub from resurfacing after it submerged in hopes of evading an Allied attack.

Scientists participating in the initial deep sea dive in 2016 noticed that all of the sub’s exit hatches were closed—a fact Hoyt says immediately made evident that all of U-576’s 45-man crew remained trapped inside, Ruane noted in a 2016 report for The Washington Post.

“[N]o matter the exact circumstances of their demise, it had to just be horrifying,” Hoyt says.

CNN’s Brad Lendon writes that U-576 rests around 30 miles off of Cape Hatteras, just 240 yards away from its final target, merchant freighter Bluefields. According to a NOAA factsheet, the cargo ship was one of 19 vessels in the KS-520 convoy, which was being escorted across the Atlantic by five Allied ships when U-576 opened fire.

At the time of this fateful meeting, U-576 was actually headed back to Germany. As NOAA’s Monitor National Marine Sanctuary portal details, the sub, then on its fifth patrol of the war, had sustained severe damage to its main ballast tank; on July 13, Heinicke radioed headquarters to announce his vessel’s imminent return. But when Heinicke saw the KS-520 convoy, he couldn’t resist launching an attack—likely because his four prior patrols had only nabbed three ships: British armed merchant Empire Spring, U.S. steam merchant Pipestone County and Norwegian steam merchant Taborfjell.

The Monitor National Marine Sanctuary notes that Heinecke ordered his crew to fire four torpedoes at the group of ships around 4:15 p.m. Three reached steam merchant Chilore and motor tanker J.A. Mowinckel, inflicting damaging but failing to fully sink the ships, while the last struck Bluefields, causing it to sink within minutes.

Meanwhile, a string of retaliatory depth charges fired by the crew of a Coast Guard cutter had dangerously damaged U-576. Upon surfacing in the middle of the convoy—a decision Ruane describes as “inexplicable”—the sub took fire from a merchant ship and two U.S. Navy Kingfisher aircraft.

Soon after, the U-boat and all of its crew vanished from sight, left to drift to a watery grave at the bottom of the Atlantic.