Hitler, as it turns out, was very skeptical of the U-boat. He told Admiral Karl Dönitz that he worried they would amount to little. Early in the war on Hitler’s plans and calls ended up being right. You can imagine pride he felt when by the time he conquered France the Wolf Packs had scored over 230 allied ships sunk.
Churchill was very worried, especially because it wasn’t just guns that the Atlantic fleet was bringing to Britain. It was butter. The rationing was so bad that at one point the Brits were rationed one egg a week. They stood in queues for hours just to get a piece of fruit. They were literally starving because food could not be brought in fast enough to feed their people, and fleet transports were being sunk faster than they could be replaced. Churchill quipped “The only thing that ever really frightened me during the war was the U-boat peril. I was even more anxious about this battle than I had been about the glorious air fight called the Battle of Britain.” That all said there were only 57 U-boats in existence when WWII began. One of the biggest surprises to hit the naval world happened on October 13, 1939 when U-47 snuck into Skapa Flow where the British fleet was anchored and sent four torpedoes into the hull of the Royal Oak. The first one landed aft and simply woke up the sleeping crew. The crew was told by commanders to relax, it was probably only an anti aircraft gun. Three torpedoes and 12 minutes later, 833 merchant marines were either drowning or burning to death in the still waters of the bay. By mid 1942, the German Kreigsmarine was sinking 700,000 tons of supplies a month. Britain was on the verge of collapse.
The daring U-Boat attack stunned the British who had the largest navy in the world and the most feared. U-47 not only sank a major battleship under their nose, they got away.
In this case, as often was the case, the U-boat crews were treated like rock stars. They were given extended
leave, girls, and gifts, publicity, and cigarettes, champagne, whatever they wanted. That was good thing for them, because the seas of the North Atlantic were awful. Storms raged all the time, the boats were tossed about for days; quarters were exceptionally cramped with 60 men cramped with torpedoes and food in a 130-foot long tube for months at a time. Men slept in the same bunks in shifts, smoked in the enclosed boats and smelled of diesel and sweat. It was dark and claustrophobic. Most of the U-boat patrolling was done on top of the waters. They dove to attack and generally couldn’t stay submerged for more than a day without having to surface and restock the air.
By 1941, the British started using perfunctory sonar ASDIC that effectively located the boat and allowed them to counterattack with depth charges. These were large cylindrical canisters with 300 pounds of dynamite that could be set to go off up to 500 feet below the surface. The U-boats could not dive more than 110 feet. The effective countermeasure forced Donitz to change tactics. It wasn’t too hard to put a U-boat down once you had an idea where they might be hiding. The shock wave of a depth charge 100 feet away would be enough to crack the hull. Also, a submerged U boat could not travel faster than a patrol vessel.
The Wolf Packs began attacking convoys at night on the surface of the water so the sonar was ineffective. It also made them harder to se and they could travel up to 15 knots on the surface. The U-Boats followed convoys during the day, formed up in long lines and radioed allied convoy positions to other boats. U-boats then swarmed the convoys and the results were devastating. By the end of the war U-boats had sunk 175 warships and 2825 merchant marine vessels. Once Germany defeated France, they had access to the seaports on the Western coastline and it made attacking convoys easier. By early 1943, Donitz was made full admiral and put in charge of the entire German navy. He had at his disposal a force of 400 U-boats, up from the 57 he started with.
However, Yankee ingenuity prevailed and newly invented airborne radar could detect the Wolf Packs patrolling the surface at night. Once American B-25 bombers pinpointed patrols, they pounded the seas with depth charges. The counter measure was so effective, the Germans were wondering they had a spy who was giving information away to the Allies. The thing about depth charges is that they are like hand grenades. Close is good enough.
By 1943 the Allies had inflicted so many losses on the Kriegsmarine that the Wolf Packs were withdrawn from the North Atlantic. In all there were 759 U-boats sunk by the Allies. About 150 were ordered surrendered but the Germans scuttled most of them instead. Most slipped beneath the waves of the North Atlantic off the coast of Ireland.
And just to remind you what it was probably like, here is a clip from Das Boot.