U Boats – ‘Grey Coffins’ That Shaped Two World Wars And Forged The Era Of The Submarine

How ‘Unterseeboots’ wreaked havoc in the Atlantic Ocean across two world wars …

The Commander never stops calculating. The basic factors in his reckoning change with each report; he must determine an escape route according to the strength of the sound of propellers and the approach angle of the destroyer. His senses no longer supply him with any immediate information; he must guide the boat like a pilot flying blind, his decisions based on indications given him by the instruments.

Against closed eyelids I see the grey-black cans twisting heavily as they shoot downward from the launches, plunge into the water, spin lazily into the depths leaving bubble trails, and then explode in the darkness – blazing fireballs of magnesium, incandescent suns.

The above passage is taken from Das Boot, written in 1973 by Lothar-Günther Buchheim and later turned into an iconic film. Although Buchheim wrote Das Boot as a work of fiction, he based it on his own experience of being embedded on a German U-Boat during the Second World War

His work paints a realistic picture of the discipline and high stakes associated with submarine service, a dark exploration of the frequently miserable and terrifying lives of the sailors that were tasked with stopping the supply convoys reaching Europe – at any cost. Winston Churchill would later say that: 

“The only thing that really frightened me during the war was the U-Boat peril.”

Das Boot, by Lothar-Günther Buchheim, was published in 1973

But what was it exactly that made the submarines used by the Imperial German Navy and Kriegsmarine so feared?

Here, BFBS unpicks over 100 years of sub-sea surface warfare and attempts to retell some of the most infamous U-Boat moments of two world wars between Britain and her allies, and Germany.

We also look at some of the more technical features of the machines and the weapons they carried, and how those weapons and tactics were combined to create a frequently deadly consequence.

Although U-Boat history can be traced to the mid-nineteenth century, much of the early story is focused upon exploration of technologies that was hoped could lead to fit-for-purpose boats, capable of conducting offensive operations beneath the waves.

And so we start our journey with U-Boats at the outbreak of World War One. At that point, Germany boasted 48 submarines across 13 classes in operation or in the final stages of their shipbuilding.

The Lusitania Disaster

The U-Boat played just as sinister a role in the First World War as it did in the second. Chief among the significance of that was the sinking of the RMS Lusitania off the coast of Ireland on May 7, 1915.

The U-Boat commander who engaged the ship did so following a decree from the Kaiser that effectively ended Prize Rules – a code protecting trade shipping during conflict - that ultimately provided authorisation to sink any ship in the waters around Britain, which the Kaiser had labelled a warzone.

On the face of it, the Lusitania was carrying passengers to Liverpool from New York, but unbeknown to many was the fact the ship was also carrying munitions that would have ultimately found their way to the Western Front in France.

The sinking of the ship was a hugely controversial matter and the loss of life impacted British communities, particularly in Liverpool where many of her crew hailed.  

RMS Lusitania arriving in New York 1907. Credit: Library of Congress

At the time of Lusitania’s construction, the Admiralty had assisted Cunard on the understanding that in times of war the ship would be used as a light merchant cruiser … she even had gun mounts on her deck for such an eventuality although they were never used. It is perhaps partly why the Germans opted to target the luxury liner in ocean waters, 11 miles off the coast of Ireland.

In advance of the ship’s final voyage, the Germany embassy in Washington had placed no less than 50 adverts in American newspapers warning passengers not to travel on the doomed ship. Alas, many did and subsequently there was a large loss of civilian life – 1,198 souls.

Although there were American losses at the disaster of the Lusitania, it did not result in the US declaring war on Germany and sending forces to Europe, this was despite the widespread repulsion of a seemingly innocent ship being targeted in the manner it was.

However, in March 1916 another civilian vessel, the SS Sussex, was attacked off the south coast of England by a U-Boat which was carrying a large contingent of Americans, and it is this event that led to the tensions and political sanctions that can ultimately be traced to the US eventually declaring war on Germany in 1917.

Following the sinking of Lusitania, anti-German sentiment spread across Britain and the USA. Here, a cartoon by American journalist Oliver Herford (1863-1935) depicts some of the negative stereotypes associated with Germany during the First World War. Credit: Cabinet of American illustration (Library of Congress) 2010716595

Massacre Of U-27 And The Battle Of Jutland

In what was not Britain’s finest hour, on August 19, 1915, the U-Boat U-27 was sunk in the Western Approaches by Royal Navy ship HMS Baralong.

Baralong was a Q ship, a heavily armed civilian vessel secretly disguised as such to cause confusion, which was sailing under the flag of the neutral United States. Using its false flag and trickery, Baralong attacked the German vessel after receiving orders from Admiralty to take “no prisoners from U-Boats.”

While survivors clambered to be rescued in the water, the crew of HMS Baralong were ordered to fire on the unarmed survivors killing them all. This extended to the survivors who had climbed aboard a rescue ship, SS Nicosian, from which American witnesses would later testify of the atrocity.

This committing of a war crime by the crew of HMS Baralong caused an international incident and following the British Government’s refusal to court martial those responsible, the massacre became a chief reason behind the Kaiser’s perusal of such deadly hostilities against civilian shipping. It was retaliation.

The outcome of the attack on SS Sussex by German U-Boat SM UB-29 on March 24, 1916 was that of harsh political sanctions being levied at Germany. Interestingly though, In response Germany did row back on its aggressive strategy against civilian vessels providing assurances to the Americans through what was called the Sussex Pledge.

This effectively returned the U-Boat’s to the former Prize Rules, pre-dating the massacre of the German crew in August 1915.

Due to the Sussex Pledge the Kaiser found his U-Boats a lesser force to be reckoned with in the seas around Britain which forced his navy into a surface action culminating in the Battle of Jutland.

Although the Battle of Jutland is recorded as a German victory, it did not result in the all out control of the seas by the Kaiser which prompted him to drop the assurances of the Sussex Pledge and return to all out war on shipping, however this time his navy placed high emphasis on the attacking of commerce, in the hope it would bring the British to a surrender. Instead, America declared war on Germany in April 1917.

Over a million tonnes of cargo was lost in the preceding months of this declaration of war.

This photograph shows the crew of the German U-Boat U-58 leaving their vessel after their surrender on Nov. 17, 1917 to the U.S.S. Fanning during World War I. Credit: Library of Congress, Prints & Photographs Division, LC-DIG-ggbain-26138 

The WWI U-Boat

Throughout this feature we are focusing on the U-Boats of Germany across both the First and Second World Wars, however it should be noted that Britain, at the outbreak of the Great War, possessed more submarines than the Kaiser’s Germany. All in all, the Royal Navy counted 80 among its massive fleet.

But because Germany was willing to use its submarines in warfare against commerce, the U-Boats of the Kaiser effectively became infamous and perhaps this is why history focuses more on them.

But what was a typical U-Boat of the Imperial German Navy equipped with?

As discussed earlier, at the beginning of the Great War Germany possessed multiple classes of submarine and as the war progressed, it continued to produce U-Boats right until the end. Most of these crafts were powered by diesel, with the exception of a very few at the start.

A limitation for the submarines of the era, not just German, was that they could not remain submerged for that great a length of time. Two hours was about the safe extent of it and interestingly, this matter did not change too much between the period of the two world wars.

In fact, there is not a lot that did change among standard U-Boats from 1914 to 1939 in terms of the technology behind their existence, a lot of which depended upon and was thanks to the diesel combustion engine. The next great leap forward would not come until the introduction of nuclear-powered submarines in 1954, save for the use of the snorkel – a tube that allowed for air intake while submerged under the surface – in 1944.

The limitations caused by matters related to the short amount of time a U-Boat could be submerged meant in reality much of the U-Boats’ terrifying work was completed on the surface, and as such, they were armed with large deck guns, some as big as 105 mm.

U-Boat SM U-38 of the Imperial German Navy. 

Writing for Military History Magazine in September 2010, the historian Stephen Wilkinson discussed the importance of a U-Boat’s deck guns. He said:

Hollywood once had us believe a U-boat’s deck guns were for fending off furious destroyer attacks after a crippled sub was forced to surface, but the truth is that powerful deck ordnance was a far more effective and less expensive way to dispose of merchant ships, which were the World War I U-boat’s primary target. No sub commander would waste a torpedo—of which he had only a limited number—on a trudging collier or rusty banana boat.

Among the Imperial German Naval fleet, there were some differences in the specifics of the armaments, crew numbers, speeds and ranges of its many U-Boats.

For example, the U-Boat mentioned earlier whose crew were massacred by the British in 1915 – SM U-27 – counted four torpedo tubes and one 88 mm L/30 deck gun. It had a crew of 35 and a top speed of 19 mph surfaced, and 11 mph submerged and had a somewhat impressive range (surfaced) of over nine and a half thousand miles – not bad for the early twentieth century.

The crew of SM U-27 were shot dead in the water by the British following the sinking of their U-Boat.

By comparison the Type UC III, built as a minelayer from 1917 had just three torpedo tubes and one 105 mm deck gun. It did however count six mine tubes for its main purposes of laying mines.

Like U-27, it had a crew of over 30 but was able to dive a little deeper than the 50 m associated with the older sub (75 m). Its range was further (11,340 miles surfaced) but this newer vessel was a fair bit slower at 13 mph surfaced, 7.5 mph submerged.

The Type UC III U-Boat

Surrender Of The Fleet

Upon the armistice of November 1918, U-Boats were required to immediately surrender. This took place for the most part at Harwich in Essex, England.  

The event was captured in the North Sea diary of Stephen King-Hall, a Royal Navy officer who would go on to become a Member of Parliament and celebrated writer. His entry of November 20, 1918 reads:  

The Harwich forces of light cruisers and destroyers left on the evening of the 18th to meet the Huns and escort them to the place of surrender, which was at the southern end of the Sledway, or about seven miles east-north-east of Felixstowe. The appointed hour was 10 a.m., and a thick fog hung over the water as the two destroyers cautiously felt their way down harbour ; but once through the boom defences it cleared somewhat, and we were at the rendezvous by 9.30 a.m. The whole time one had to pinch oneself to make sure that one was really out there to collect U.-boats and that the whole thing was not a dream. Suddenly a British Zepp droned out of the mist, circled round and vanished again to the northward.

King-Hall’s diary entry continues:

We were received by the German captain together with his torpedo officer and engineer. They saluted us, which salutes were returned.

" Do you speak English? " said K--. 'Yes, a little,' replied the Hun. 'Give me your papers.' The German then produced a list of his crew and the signed terms of surrender, which he translated into English. These terms were as follows:

(i) The boat was to be in an efficient condition, with periscopes, main motors, Diesel engines, and auxiliary engines in good working order.

(2) She was to be in surface trim, with all diving tanks blown.

(3) Her torpedoes were to be on board, without their war-heads, and the torpedoes Were to be clear of the tubes.

(4) Her wireless was to be complete.

(5) There were to be no explosives on board.

(6) There were to be no booby traps or infernal machines on board.

This captain was a well-fed-looking individual with quite a pleasant appearance, and he was wearing the Iron Cross of the first class. He had apparently sunk much tonnage in another boat, but had done only one trip in U.90. Curiously enough, his old boat was next ahead of us going up harbour K-- then informed him that he would give him instructions where to go, but that otherwise the German crew would work the boat under the supervision of our people. This surprised the Hun, who showed us his orders, which stated that he was to hand the boat over to us and then leave at once for the transport. His subordinates urged him to protest, but he was too sensible and at once agreed to do whatever we ordered. The German crew were clustered round the after-gun, taking a detached interest in the proceedings.

The entry on this date ends with a description of the respect and honour the enemies still held for each other, and the traditions of the seas. It says:

At 4 p.m. a motor-launch came alongside and the Germans were ordered to gather up their personal belongings and get into her. The captain, without a sign of that emotion which he must have felt, took a last look at his boat and saluted. We returned his salute, he bowed, and then joined his crew in the motor-launch, which took them to the destroyer in which they made passage to the transport outside.

During the First World War, the Imperial German Navy had succeeded in sinking over 5,000 vessels using their fleet of U-Boats.

Signed in the Treaty of Versailles, an outcome of losing World War One was a directive that limited the tonnage of the German fleet and a ban on the building of submarines. However, as the inter-war years progressed, Germany secretly began the rebuilding of her U-Boat fleet, and by the time World War Two commenced, she counted no less than 65 to her name.

First Man To Ever Storm Nazi U-Boat And Capture Enigma Machine Dies
A U-Boat of the Second World War (U1 10) and HMS Bulldog

The Battle Of The Atlantic

The Weimer Republic was restrained under the Treaty of Versailles where ship building, and the holding of military forces were concerned. However, when Adolf Hitler came to power in the early 1930s, he ordered the building and amassing of strengthened capability, which included the production of the largest U-Boat fleet in the world heading into 1939.

It is thanks to this that the longest continuous battle of the Second World War occurred – the Battle of the Atlantic.

The peril faced by the crews of the North Atlantic convoys is undisputed. Their plight has been retold, not least in the movies. In 2020, this was the case in Greyhound, a film written for the screen by Tom Hanks who also starred in the leading role. A cornerstone to the plot of Greyhound is that in the centre of the ocean, the convoys had to pass through an area that was not reachable by aircraft and thus, most vulnerable to U-Boat attack.

In the opening months and years of the war, U-Boats were effective in locating and destroying ships carrying essential war cargo to England and Europe, largely thanks to this area of no air cover.

In response, the allies advanced technology to aid the convoys, and their protection vessels – like those depicted in Greyhound – in locating the silent, underwater U-Boat threat.

This in turn resulted in the U-Boats developing a strategy which saw them fighting in what was known as Wolfpacks. These Wolfpacks mercilessly hunted down thousands of ships throughout the six years of the Battle of the Atlantic.

The number of Allied losses on the ocean slowed after the entering of the war by the USA. However, it was still a deadly theatre to have to operate in, and by the time the war ended in 1945, 72,000 Allied lives had been lost.

The opening page of the 1973 Lothar-Günther Buchheim book Das Boot, like the film version’s opening scene, tells us that:

“Of the 40,000 German U-Boat men in World War II, 30,000 did not return.”

Type VII and Type IX U-Boats at Trondheim, Norway, 19 May 1945.

How Did The Torpedo Work?

The torpedoes Kriegsmarine U-Boats used throughout the Battle of the Atlantic were responsible for the sinking of 3,000 Allied ships.

The early versions worked in one of two ways. If the torpedo was fitted with a pistol trigger that relied on impact, the warhead would explode upon meeting the hull of a ship (or another solid object).

But, if they were fitted with a magnetic trigger, the warhead would be exploded whenever the magnetic field around the torpedo changed once released.

This proved the deadliest, as it meant torpedoes could be released to come into the closest magnetic contact with a target while under the keel of a ship. The resulting shock wave from the explosion would be enough to rupture a ship’s keel.

Another and more advanced torpedo entered service later in the war which allowed the Germans to phase out the frequently problematic magnetic-triggered version.

This new weapon, the G7 Torpedo, worked acoustically, running a distance before arming itself and then turning towards the closest and loudest thing around it. But this new technology was not a silver bullet and it is thought that at least two U-Boats were lost due to their own torpedoes turning on them and detonating.

The age of the submarine really cemented itself in military terms during the Battle of the Atlantic.

Both sides scrambled their scientists and weapons experts to advance, inch by inch, the methods that both aided detection and frustrated it.

During this period, both sides fine tuned and improved their Sonar abilities. The Allies introduced Radar and to counter it U-Boats were fitted with radar warning receivers.

For the U-Boats, the introduction of the snorkel allowed for batteries to be recharged and for air to be supplied to a still submerged crew – making them evermore stealthy. But the Allies responded by further improving their own detection methods yet again that even allowed for them to spot a snorkel mast beyond the range of visual detection.

Type VII at Labone where today it acts as a museum. Credit: Darkone @ Creative Commons

A Close Look At The Type VII Submarine – The Workhorse Of The German U-Boat Fleet

In total, 703 Type VII U-Boats were produced, and many remained in service with other navies after the Second World War ended. The last Type VII to retire was in 1970. It was the most widely used type of U-Boat throughout the Battle of the Atlantic.

Top speed:    20.4 mph surfaced, 8.7 mph submerged

 Range:         9,800 miles surfaced, 92 miles submerged

Max depth:    230 metres (tested)

Crew:            52

Armament:   5 x Torpedo tubes with a total of 14 Torpedoes or 39 mines and 1 x 88 mm C/35 naval gun with 220 rounds

Operation Deadlight

At the end of the Second World War, the Royal Navy took receipt of 156 U-Boats and moored them in two locations, off the coast of Northern Ireland and at Scarpa Flow, Scotland. Operation Deadlight was the name given to the scuttling operation undertaken to dispose of the captured vessels.

Of the 156 U-Boats surrendered, 116 were eventually scuttled.

The Royal Navy plan was to tow the vessels to sites in the Atlantic off the coast of Ireland and use them as practical targets for bombing runs by the Royal Air Force. Others would be destroyed with naval guns and some by placing explosive charges in their hulls. However, the operation turned farcical when seveal U-Boats sunk while being towed out to sea due to poor conditions they had fallen into while being moored up and exposed to the elements.

All captured U-Boats earmarked for scuttling were disposed of by February 11, 1946.


Forty-two surrendered U-boats moored at Lisahally, Northern Ireland, June 1945. Credit: Crown

The golden age of the submarine may have entered the autumn of its year due to increasingly improved detection methods and technologies that exist in the modern day.

This is something former chair of the UK Foreign Affairs Select Committee Crispin Blunt MP discussed in an interview with BFBS to mark the 75th anniversary of the first atomic bombing. In it, Mr Blunt described the situation around submarines and their inability to remain undetected: Mr Blunt said:

“The whole concept proceeds on the basis that the submarine is invisible, yet four years before I made that vote, there was a submarine research warfare scientist, a senior NATO position, gleefully proclaiming the end of the submarine because accusation technology was advancing geometrically and (had) the ability to pick up all the signals that a submarine gives off, whether it’s heat, movement or nuclear signal."

If it is the case that submarines may one day soon become obsolete in their stealthy nature and nations like the UK and USA are no longer prepared to use them as the means to house their respective nuclear deterrents, than perhaps history will look back at the two conflicts of the twentieth century - both impacted considerably and shaped by the U-Boat - as the submarine's true golden era. 


Das Boot by Lothar-Günther Buchheim is available in paperback by Orion.

Thanks to US Library of Congress - an extensive collection of historical images, paintings, articles and newspapers are available to be viewed online at www.loc.gov