U-2511, or How A Submarine Changed the Course of the Cold War Without Firing a Shot

An oft-ignored (much to my bemusement) aspect of the Cold War was the silent undersea conflict. Submarines, both NATO and Soviet, played cat and mouse, conducted espionage and made preparations for war, and formed a critical part of each side’s strategy. Subs snooped for electronic emissions, tapped cables, and tailed each other in a continuous effort to gain advantage over their colleagues in someone else’s Silent Service. Submarines became a critical part of the so-called Nuclear Triad, of land-based intercontinental ballistic missiles, airborne bomber aircraft, and submarines mounting long-range missiles of their own, hiding quiet, deep, on patrol and always ready for a devastating, impossible to kill second strike capability. Submarines practiced infiltrating each other’s home waters, and doing rude things like sinking warships and transports, firing missiles at hapless targets, both on land and at sea, and slinking away without a trace. All of this, the espionage, the wargaming, the fundamental approach to submarine warfare, started with one submarine’s fateful patrol in the final days of World War II.

The Battle of the Atlantic, the effort of Nazi Germany to starve the United Kingdom into surrender, and the Allied effort to prevent such a disaster, formed much of the Second World War’s strategic calculus in the European theater of operations. While the British Royal Navy reigned supreme on the surface, something the Kriegsmarine did not even bother to challenge, the Ubootwaffen, the elite German submarine community wreaked havoc from below. Across the war, 1174 U-boats would claim 3600 merchantmen, over 14 million tons of shipping and 175 warships. Numbers, however, do not tell the whole tale.

For much of the war, the Germans used Type VII and Type IX submarines, prewar designs able to remain submerged for a few hours, up to about a day if a commander was careful with his oxygen supply. In essence, the submarines were not true subsurface warships, only submerging to evade attackers or to prosecute torpedo strikes against vulnerable targets. When submerged, submarines were badly hampered, relying on periscopes and primitive passive sonar (think underwater microphones) to maintain awareness of the world around them. They were also much slower, a surfaced sub able to make about 18 knots, versus 6 knots submerged. Ironically enough, submarines for much of the war found great success on the surface at night, using their tiny profiles to avoid detection until they had begun attacking a convoy. By 1943, matters had changed significantly.

The first thing that affected the way the world looked at submarines was actually a Danish invention from about 1938. The experiments involved a system of pipes submerged subs could raise while they were near the surface, allowing an air exchange. Originally adopted by the Kriegsmarine to resupply crews with fresh oxygen, by 1943, improvements in Allied radar meant the snorkels were adapted to allow a U-boat to operate her diesel engines underwater, charging the batteries for the electric motors normally used when submerged. This gave the submarine effectively unlimited underwater range, if meaning regular intervals close to the surface to charge the batteries on the extremely noisy diesel engines.

The second innovation should have entered service in 1943. Its name was the Type XXI submarine, typified in U-2511, one of only two in the class to make a war patrol. The Type XXI was a radical German advance, and had it entered service on schedule, might have affected the course of the war. In May of 1943, while the war in air was firmly in the Allies’ favor, the war at sea was only starting to turn. Winston Churchill was advised that with current Allied convoy losses he had about six weeks before shortages in the United Kingdom might begin to put serious pressure on the populace, possibly leading to a negotiated surrender. As luck would have it, this was also about the time American shipyards hit their stride in production both of merchantmen and escort warships, even as the U-boat fleet began suffering greater and greater losses. U-2511 might have changed all of that.

The Type XXI submarine was the first submarine designed to spend the majority of its time submerged, instead of on the surface. Equipped with a new passive sonar, the submarine could easily “see” without ever surfacing. With the new Danish snorkel, it need never surface to run her diesel engines, and her new batteries and electric motors gave her incredible underwater range and speed, up to 16 knots, more than fast enough to evade Allied convoy escorts. With a new streamlined design, not only was the sub swift underwater, but difficult for Allied radar to detect surfaced (it is not known if this stealth was intentional or not.) The Type XXI represented the way forward for combat submarines, equipped even with such luxuries as an automatic loader for its six torpedo tubes and a refrigerator for fresh foodstuffs.

Unfortunately for the Kriegsmarine, events conspired against the Type XXI, like so many other Nazi wonder weapons. The subs were not favored by Karl Donitz, commander of the U-boat fleet, whose tactical acumen had kept many Allied convoy commanders on the back foot. The lack of a priority hampered the allocation of limited Nazi resources to the new boats. Also, the submarines used a pioneering method of construction that backfired. Each boat was constructed in ten pieces, built in hardened underground factories, then assembled in special, hardened sub pens deep in German territory. That was the first questionable decision, as the submarine’s ten individual pieces now have to be made to actually fit together (as any industrial designer or engineer knows, much harder than it sounds). The second questionable decision was the choice of labor force, namely the slave populations of several Nazi work camps. Suffice it to say that motivation was lacking, and quality control issues followed, to no one’s great surprise but the Germans. Thus U-2511, the first Type XXI ready for war, did not set sail until April 30, wait for it, 1945.

U-2511, nor her sister U-3008 who sailed on May 3, ever got the chance to fire their weapons in combat. However, that does not mean they did not exert a very tangible influence on postwar science and politics. U-2511 actually encountered a British anti-submarine hunter group on May 5, the day after receiving the ceasefire order. In a practical demonstration of the submarine’s incredible ability, she tailed the ships for six hours, coming within 500 yards of the cruiser HMS Norfolk, before quietly slipping away without being detected. When U-2511 was transferred to Lisahally, Ireland for internment, she was escorted by HMS Norfolk, whose crew couldn’t believe U-2511’s exploits and claims, until comparing log books. This was but the first of the shakeups these incredible subs would cause.

Eight finished Type XXI’s were divided among the victorious Allies, one for the UK, one for France, two for the US and four for the USSR. All were thoroughly examined and carefully studied, with the advances rapidly integrated into the Allied fleet. USS Cochino, lost to a battery fire and explosion in 1949, was one of a new generation of enhanced submarines, with German technology incorporated into them, conducting some of the first operational training and espionage with the new capabilities. A new snorkel, allowing the sub to run its diesel engines and recharge its batteries, newer, more powerful batteries and new, more capable sonars were all included her design, all adaptations of the new German technologies pioneered by U-2511. Western intelligence analysts after the war worried that should war break out with the USSR, they would be able to rapidly put the type into mass production, a major issue as they were still incredibly difficult for current sub-hunting ships and aircraft to defeat. The type influenced all conventionally powered submarine designs to follow, with three Soviet classes practically evolved clones of the design, some of which are still in service today (albeit with North Korea).

Above all, the Type XXI’s redefined what it meant to be a submarine. No longer were submarines underarmed surface ships with an exotic defensive ability, nor scientific and engineering curiosities not worthy of serious military attention. The Type XXI validated the submarine as a capable, long-range, subsurface warship to be feared and respected by navies the world over. Without the Type XXI’s incredible leaps forward to lead the way, we could only guess how submarine and naval technology wold have evolved to date. They were such incredible vessels that in 1957 West Germany salvaged U-2540, a scuttled Type XXI, renaming it the Wilhelm Bauer, and used it as an advanced research and prototyping vessel until 1982. She is now on display as a museum ship in Bremerhaven, Germany. She represents an incredible advance and a testament to the engineers and tacticians that dared to push the envelope and change the world, even if their brainchild never did fire a shot in anger.



  1. Excellent write-up. I’m a huge U-boat geek (visited the U-2540 twice – as well as the U-995 in Laboe and the U-510 in Chicago), so this is right up my alley 🙂

    Liked by 1 person

    1. This is essentially an excerpt from an older, far longer essay detailing how close the Kriegsmarine came to winning the war with the U-boats and the fascinating history of that all-but-untold war. Expect a follow-on series exploring those subjects.

      Liked by 1 person

      1. Great – looking forward to reading it.

        This is one of the books I took with me on my honeymoon: https://books.google.nl/books?id=hHV9AgAAQBAJ

        The last 150 pages or so are all about how the XXI shook up not just ASW tactics, but the entire naval strategic planning of the Cold War era. Highly recommended, if you like that sort of thing.


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