On April 16, 1944, while on its first deployment, U-550 attacked the tanker ship SS Pan-Pennsylvania. The Pan-Pennsylvania was at that time the largest tanker in the world, carrying a cargo of 140,000 barrels of aviation gasoline. The tanker had fallen behind the rest of her convoy that was making its way from New York to Great Britain, making her an inviting target. The torpedo attack set the cargo on fire, killed 25 of the Pan-Pennsylvania's crew of 81, and eventually sink the huge tanker. While the escort destroyers USS Joyce (DE-317), USS Gandy (DE-764), and USS Peterson (DE-152) went to work rescuing the surviving crew, U-550 hid under the mayhem.
As the Joyce was about to withdraw, the German submarine moved from its hiding place and was picked up by sonar above. Joyce laid a spread of 13 depth charges that drove U-550 to the surface. The crew of the U-boat meant to fight it out and began to fire its deck gun at the American ships. All three escort destroyers returned fire, with Gandy moving to ram the soft target of U-550's conning tower. The German sub's attempt to move out of the way caused Gandy to strike about 30 feet from the stern. Meanwhile, Peterson dropped two more depth charges that exploded near the submarines hull. The U-boat's guns were silenced. Joyce hailed the Germans, demanding they abandon ship. With his vessel doomed, the German commander chose to scuttle his boat rather than let it fall into American hands. Another explosion was heard, only this time from within the hull of the German submarine. Only 40 minutes after the Joyce had first detected her, U-550 was sunk. The USS Joyce was only able to find 13 surviving Germans, one of whom died while in route to England.
A little over 68 years later, on July 23, 2012, the wreck of U-550 was found by a private group of shipwreck hunters funded by Joseph Mazraani, a successful attorney from New Jersey. Some of the members of this group have been searching for this wreck for two decades. They are currently working on a project to document the wreckage of ships from the Battle of the Atlantic. To see some great pictures taken of this engagement during WWII and some links to videos, visit the Discovery Channel page for this event. If you are not familiar with this part of WWII naval history, I've picked out an excellent video (10 minutes, in color!) for you, courtesy of YouTube: