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By Michael C. Barnette
Following Hitler’s defiance of the Treaty of Versailles in 1935, Germany implemented a brisk and aggressive remilitarization program. However, rather than pursuing new technology and taking the time to produce a modern submarine force, Germany initially opted for quantity over quality. To expedite the rebuilding, the proven U-boat designs from World War I were hastily modified to manufacture the conventional Type VII and IX U-boats. Initially, the U-boats scored numerous victories. Yet, by 1942, the “Happy Time” enjoyed by U-boat crews earlier in the Atlantic had all but vanished. Convoy protection, improved sonar detection, and Allied air cover inflicted heavy casualties on the Unterseebootwaffe. The conventional U-boats were simply too slow and could not stay submerged long enough to avoid being rapidly sent to the bottom by the Allies.

Following a November 1942 meeting aimed at rectifying the disturbing trend of U-boat losses, two engineers proposed a simple solution: increase the submarine’s battery supply. By increasing a submarine’s battery supply, speed and endurance could be improved. Currently, the conventional Type VIIC U-boat could travel at six knots for approximately 45 minutes or two knots for approximately 20-30 hours, before surfacing to recharge the batteries with her air-breathing diesel engines. By doubling the battery supply in a secondary hull, the new elektroboote could maintain a speed of 18 knots for 90 minutes or five knots for 60 hours. The design of the new Type XXI electroboat was completed in July 1943, with a planned delivery time of the first vessels expected by the end of 1944.
Braced by supports, this German Type XXI U-boat rests in dry-dock following its surrender to Allied forces.”
While speed and endurance were the two most critical improvements in the Type XXI design, other technological advances were also incorporated into the new submarine. Currently, when a conventional U-boat found abundant targets to attack, she was limited to the amount of torpedoes she could fire before retreating and having to manually reload her tubes. This was especially critical considering that the Type VIIC and IX U-boats had to surface to gain access to additional torpedoes carried between their inner pressure and outer hydrodynamic hulls, which left them fairly vulnerable to attack. The Type XXI addressed this shortcoming by possessing six bow tubes and a semi-automatic hydraulic loading system that could fill all of the bow tubes in approximately 20 minutes. The electroboats also utilized radar, radar detection, and a new sonar device. The Gruppenhorchgerät sonar array, which utilized 48 receivers in a housing mounted below the bow, was capable of detecting a target as far away as five miles and at a cruising speed of 11 knots, though there were initial problems with interference and streamlining. Improvements were also made that allowed the Type XXI to keep her depth more accurately, a constant problem on conventional submarines. Additionally, the crew was treated to the presence of a deep freezer, which kept food from quickly spoiling on their long sojourns across the Atlantic. Furthermore, it is important to note that the Type XXI U-boat was the first production submarine to also abandon deck-mounted guns in favor of improved streamlining, a characteristic that was eventually adopted by all other submarine navies. The elektroboote was truly the first modern submarine.
Photo: The U-2513 rests on the sandy sea floor lying hard over on her starboard side. Explorer Richie Kohler hovers over the port side fixed stabilizer surface located just forward of the large three-bladed screw.
The U-2513 was built in late 1944 at the Blohm and Voss shipyard in Hamburg, Germany. The Type XXI program implemented a fairly efficient modular construction process. Each electroboat was constructed from eight separate sections, allowing the vessels to be completed in approximately six months, including only 50 days on the rails. While other Type XXI U-boats suffered delays due to Allied bombings, it is unclear if the U-2513 suffered any damage during its construction. In March 1945, the U-2513 sailed from Kiel, Germany to Norway under the command of Fregattenkapitän Erich Topp, former commander of the U-552.

Unfortunately for the German war effort, the Type XXI U-boats were introduced too late in the war to make a difference. Only 119 electroboats were commissioned, and fewer still were actually war-ready. Before making any war cruises, the U-2513 was surrendered to the Allies in May 1945. The U-2513 was initially taken to the British naval base at Lisahally, Ireland. There, along with 62 other German submarines, the U-2513 and her crew awaited their fate. At the same time, a special detachment of approximately 200 U.S. submariners called the Rainbow Division was formed to learn the technology of the U-boats and sail some of them back to the United States. Thirty-eight officers and men departed New London, Connecticut, and arrived in Northern Ireland to take over the U-2513. They spent about a month learning the Type XXI systems and controls, a process that was complicated by the fact that the U.S. sailors had to learn German along the way. After everything was checked out and drills were successfully conducted pier-side, the U-2513 went to sea for more trials. Comfortable with the U-boat’s operation and performance, the crew of the U-2513, part of the “Forgotten Submarine Bastards of Ireland”, departed Lisahally with the U-3008 and sailed for the United States in August 1945. Also onboard were eight of the original German crew of the U-2513.

The U-boats cruised on the surface for the majority of their initial trip to Newfoundland, though a couple of trim dives were made. Just before arriving in Newfoundland, the U-3008 flooded her stern and had to be towed in. The two Type XXI U-boats then sailed for New London, Connecticut, and finally to the Portsmouth Navy yard in New Hampshire, where the U-2513 was commissioned into the U.S. Navy as the U.S.S. EX U-2513. During the three month stay at Portsmouth, the U-2513, now called the TATAO (Things Are Tough All Over) by her crew, spent most of the time in the yard for inspection and overhaul. After her time in the yard, the submarine operated out of New London, conducting numerous tests.
Top: President Harry Truman (in the light suit and hat) disembarks U-2513 after his historic dive off Key West in 1946.

2nd Down:
The U-3060 in the final stages of construction at the Deschimag AG Weser yard following an Allied air attack. Note the GHG sonar housing below the bow.

3rd Down:
Shipyard workers install the massive starboard diesel engine in section 3 of a Type XXI U-boat.

Bottom:
A view of the forward torpedo room in the U-2518 after the war. An operator is perched in between the middle two tubes and in front of the adjustor device for Lagenunabhängiger torpedoes.
In April 1946, the U-2513 sailed for Key West, Florida. In November, President Harry Truman boarded the U-boat and participated in a cruise to 450 feet. This cruise would represent only the second time a President of the United States would travel underwater in a submarine, the first occurring on August 23, 1905, when President Theodore Roosevelt made a series of short dives onboard the archaic torpedo boat, U.S.S. Plunger. The log of President Truman’s November 17-23 vacation to Key West even mentioned the many technological advances of the German U-boat, such as the advanced snorkel design that allowed the boat to stay submerged for extended periods of time. After breakfast was served on the boat, the U-2513 commenced diving operations at 9:30 a.m. on November 21. After descending to 450 feet for a minute or two, the U-2513 ascended to periscope depth by 10:00 a.m. However, during this time, the port engine room flooded, which resulted in copious amounts of smoke to creep through the aft portions of the sub. Fortunately, the situation was addressed and the U-2513 safely surfaced at 10:15 a.m. The trip earned President Truman a card signed by the U-2513’s commanding officer, Lieutenant Commander James Burr Casler, which certified that Truman was now an “Honorable Member of the Ancient Order of Deep Dunkers.”

John Cunningham was one of the few fortunate sailors to have the unique experience of sailing aboard the former German U-boat while she served in the U.S. Navy. He reported to duty in early 1949 to find the submarine already “Americanized,” in that many of the German instructions and labels mounted on equipment had been swapped out for English versions. Having also served on the U.S.S. Diablo (SS-479), his recollection of the submarine illustrated the vast improvements of the Type XXI design over its American counterparts. Built about the same time, the Diablo was bigger, slower, and not as well armed. It was not until around 1950 that the U.S. Navy had an equivalent design of her own.

Photo: Explorer Richie Kohler peering into an open hatch on the forward hull of U-2513. Note the small size of the hatch and imagine the difficulty af gaining access wearing full technical diving equipment.
By mid-1949, even with a cracked pressure hull that prevented the submarine from descending past 400 feet, Cunningham came to appreciate the advanced design and engineering of the submarine. Interestingly, he noted the extraordinary hull paint on the U-boat, which seemed to hold up extremely well as compared to the hull paint on other U.S. Navy vessels. Typically, period fleet boats were scraped and painted about every three months to prevent rusting. However, by 1949, the U-boat was still wearing her original hull paint. When ordered to scrape the hull, the crew found the task extremely difficult, as the paint would simply not come off. After extensive work, the paint came off one scratch at a time. Underneath, the metal was bright and shiny, just as it may have appeared when built in 1944. However, after being repainted with standard Navy hull treatment, she was rusting within a few months.

During his short stay on the U.S.S. EX U-2513, one event in particular stood out in Cunningham’s mind. During operational tests, the submarine experienced a “hot run” of one of her torpedoes. Instead of leaving the torpedo tube, as any well-mannered torpedo is apt to do, this torpedo chose to stay put and run in the tube. At the time, most of the young and inexperienced crew did not know what was amiss. Fortunately, one of the crew in the torpedo room was a veteran submariner who served in World War II. When the commanding officer strolled forward to determine what was going on, obviously oblivious to the impending danger of an armed weapon in the torpedo tube, the crewman screamed to him: “Get your [expletive deleted] ass back to the Control Room and put a down angle on this boat and get rid of this torpedo!” Fortunately, the officer heeded the enlisted man’s advice and averted a potential disaster.
After three years of service in the U.S. Navy, the U-2513 was towed northwest of the Dry Tortugas to be used as a target. On October 7, 1951, the destroyer U.S.S. Robert A. Owens sent the Type XXI U-boat to the bottom following several salvos of anti-submarine rockets. Supposedly, Navy divers visited the wreck in the 1950s, but recreational divers did not visit her remains until almost 1990. Billy Deans occasionally ran charters to the wreck in the early 1990s while his shop, Key West Divers, was in business. Presently, no regular charters to the U-2513 are available due to her remote location and depth.

The elektroboote now sits in 214 feet of water, with damage both fore and aft of the conning tower. Part of her sail lies in the sand off to the starboard side, with hedgehogs (anti-submarine weapons) residing along the port side. The U-boat sits with an almost 60 degree list to starboard. Numerous valves and pipes are visible running along the pressure hull as the majority of the hydrodynamic outer hull has deteriorated. Heading aft, divers can observe massive damage to the hull just forward of the engine room. At the extreme stern, both screws are visible nestled amongst the large diving planes and rudders. Forward of the conning tower, a large hole on the port side allows access to the forward torpedo room. Proceeding forward, divers can pass equipment that has tumbled across the interior. A ladder to an open deck hatch lies under a coat of rust and silt. The torpedo tube doors are easily visible, and the perimeter of the room is adorned with numerous placards, gauges, and hand wheels. The forward conning tower hatch is open but, due to the tight fit, there is no diver access. For those that have the diving experience and are willing to make the journey, the wreck of the U-2513 presents a unique opportunity to inspect one of the few remaining examples of a Type XXI U-boat, the first true modern submarine.
Close-up view of the circular radio direction finder aerial on the conning tower of the U-2513.
Michael C. Barnette is the founder and director of the Association of Underwater Explorers (http://uwex.us), a coalition of divers dedicated to the research, exploration, documentation, and preservation of submerged cultural resources. Employed as a marine ecologist with the National Oceanic and Atmospheric Administration, he has published two books: Florida Shipwrecks and Shipwrecks of the Sunshine State: Florida’s Submerged History.
The long bottom time spent to exploring the U-2518 requires a diver to spend over an hour and a half decompressing before he can safely surface. During the 90 minutes the divers were entertained by a pod of playful dolphins.