Your correspondent took the opportunity once to look through a navy submarine – safely on the surface, in a harbour. It was impossible to avoid the thought that this was one of the dumbest things ever invented, to put men under the waves to kill other men. What a stupid waste of pipes, pillows, cups, wires, bulbs, handles, toilet paper, etc, not to mention all those technical things. Now, engrossing page after engrossing page, we take a vicarious “Dive, dive!” into the deep blue, and it’s just as scary and mad as we always thought it would be.

These are Germany’s U-boatmen because, Moorhouse reasons, the standard narrative, especially in the English-speaking world, is told almost exclusively from the perspective of the Allies, by the merchantmen in the convoys and their destroyer escorts. Instead, here are the attacks, explosions, deaths, perils, fear, disasters, heat, cold, filth, spoiled food, “U-boat stink” and boredom of the Nazi crews; and not least what they actually thought about it all.

Moorhouse’s focus, then, is the human side of the story and the grim realities faced, the horrors of combat and the psychological damage that was wrought. Thus emerges a story of individual bravery, of unimaginable endurance, of technological advances and strategic setbacks. Uiltimately, too, of failure, loss and defeat – of the 40,000 U-boat men, only 11,000 are thought to have survived, a death rate of nearly 75 per cent.

This is the highest ratio in any other branch of service, in any army, in any theatre during the six years of hostilities of the Second World War. And, as the author points out, for more than 95 per cent of the almost 30,000 young Germans killed, their only grave is the seabed.

Of the 782 U-boats sunk, 429 yielded no survivors and no bodies. Disappeared with no trace, no personal effects, the crews’ loved ones were left to endure an agonising absence.

More than a third of the German submarines lost were on their maiden patrol. The lifespan of the average U-boatman could be just one and a half war patrols. Poor leadership, inadequate training and exhaustion all contributed. For a sinking U-boat taking on water after severe damage from depth charges or enemy firing, it meant a catastrophic failure of the hull, crushed by the water pressure, and death by drowning, slow or mercifully quick.

The men left behind them formidable statistics, claiming a bitter harvest among Allied shipping by sinking almost 3500 Alled ships for a total of almost 15 million tonnes. If the figures are difficult to comprehend, this was nearly 70 per cent of Allied shipping losses in all the various theatres of war. As is recalled, British Prime Minister Winston Churchill remarked that the U-boat threat was the only thing that really frightened him during the war.

Still, as Moorhouse tells it, while early Allied losses of merchantmen seemingly provoked a visceral fear of collapse, Germany’s submariners were surprisingly ineffective. A reappraisal of the statistics, and the incorporation of the German perspective, shows that the reality was much less, and the U-boats of the Kriegsmarine, the German navy, never came close to hitting their ambitious targets. By war’s end, the Allied merchant fleet had actually grown to nearly 40 million tonnes, more than twice the size of the British fleet at the outset.

“When there was a genuine opportunity to disrupt Atlantic supply lines, prior to the American entry into the war in December 1941, Germany’s U-boat force lacked the numbers to successfully press their advantage,” the historian writes. “And, by the time that it had the numbers, the industrial and military might of the US meant that the U-boat’s moment had already passed. For all the hardships endured, and the horrors inflicted on the enemy, the U-boat was shown to be a blunt weapon, a bloody and elaborate failure.”

“Wolfpack” sets the scene briefly with the Great War of 1914-18 when submarines were among several new inventions that had arrived to slaughter people on an industrial scale (along with tanks, warplanes, machine guns, poison gas, flamethrowers, Zeppelins and more – editor). But Germany lost the war, and from November 20, 1918 the surviving German submarine fleet of 176 U-boats crossed from Europe to surrender off the English coast.

However, Germany wasted little time in seeking to evade the punitive restrictions placed upon it by the Treaty of Versailles in 1919-20. Already in 1922 German shipyards would clandestinely develop submarines and thus maintain essential technical and design staff. A dummy company was set up in Holland, and vessels would either be built under licence or for sale on the open market. In this way, one was built for the Turkish navy in 1928 and another three under licence in Finland. By the time these four vessels were being brought into service in Germany in 1933, the Nazis were effectively tearing up the treaty and re-arming all round, having a force of 16 U-boats and establishing a submarine school.

By 1939 Karl Dönitz took command of the 1st U-boat Flotilla and went to war with 56 submarines rather than the force of at least 300 he wanted. Only 22 were suitable for service in the Atlantic, where convoys crossed from North America. A typical crew was a handful of officers and some 50 men, initially carefully selected and put through very rigorous training. Such resilience and character was perhaps less prized in other military arms.

At first the Germans enjoyed halcyon days, their so-called “Happy Time”, sinking much Allied shipping. Interestingly, initially the “Battle of the Atlantic” was undoubtedly the “cleanest” theatre of the war, with many more examples of the old-fashioned “solidarity of the sea”, namely helping or rescuing survivors of sinkings, than there were instances of atrocities.

However, as the war became more desperate and vicious this code was discarded. Allied countermeasures improved, German losses grew and the stringent entry requirements for crew were all but abandoned. Clever propaganda had extolled the glamour of joining a U-boat but not the actuality. Early enthusiasm crumbled and morale dipped. Many men were helplessly seasick or panicked at the first real action and were useless, glad to be captured.

The Third Reich cared little about profound psychological damage, or “combat stress”, but away from the propaganda a few navy doctors were studying the symptoms, such as insomnia, dizziness, incontinence, night terror, nervous tics and apathy. The hardships could produce a collective hysteria known as Blechkoller, or “Tin Can Rage”; shouting and fisticuffs.

When the British seized an Enigma code machine and learned its secrets, they had foreknowledge of the location and intention of Dönitz’s fleet and could divert convoys from danger. Also, by the time of the attack on Pearl Harbour on December 7, 1941 that brought the United States into the war, American naval forces had been engaged in an undeclared war in the Atlantic for more than six months. The Germans failed to break the Allied supply lines and in May 1943 Dönitz mostly withdrew to the safer Caribbean and Indian Ocean. After a late flare of false hope of revival, the defeated U-boats were scuttled in ignominy.

“Wolfpack” is a terrific book, chock-full of great stories and detail. For instance, the toilet that sank a sub, the Irish seaman rescued from the sea by the German U-boat that had sunk his ship but which he thought was English because the commander and his Italian passenger were conversing in English, and “weddings” on board.

Moorhouse has penned a refreshing change from the oft-told war tales of Dunkirk, the Holocaust, Arnhem, D-Day, Operation Barbarossa, Stalingrad, Colditz, etc, etc.

Scary yes, mad yes. But in the end, just what was it all for?