Danger in the deep: Battle of the Atlantic

Jonathan Dimbleby's new book tells the story of the Battle of the Atlantic. He explains to Rob Attar how German U-boats nearly changed the course of the Second World War, and why salvation for the Allies came from the skies...

British ships on convoy duty in the North Atlantic

How important was the battle to the outcome of the war?

It was fundamental. The Atlantic was the route by which all resources came to Britain, without which the country would have collapsed. Had we lost the battle, we wouldn’t have had enough weapons – nor the industrial capacity to make weapons – and American troops would not have been able to get across for D-Day. In fact, there wouldn’t have been a D-Day.

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Was it possible that the Allies could have lost the Battle of the Atlantic?

With the benefit of hindsight it’s clear that we were likely to win, but at the time it appeared that we could very easily lose. Had Hitler not been so obsessed with the urge to conquer Russia, and instead diverted more resources to the Atlantic, it could have been a very close-run thing.

To my mind it’s academic whether we could or couldn’t have lost, because what is intriguing is that it was an open question for so long. With all the demands on ships elsewhere, it took only a small number of vessels to be lost in the Atlantic for the reduction in supplies to inhibit the ability to wage war. Winston Churchill claimed that nothing caused him greater anxiety than the U-boat threat, while President Roosevelt said that the war would in the end be won or lost in the Atlantic.

At the start of the battle, which of the two sides was best prepared?

Neither was very well prepared. The British came to the battle having misread the lessons of the First World War – when U-boats first displayed their destructive potential – and they underestimated their capacity to damage Allied routes across the Atlantic. They did not have enough escorts to protect their ships, and were torn between that requirement and the need to protect against invasion across the Channel. There just weren’t enough ships to go round.

As for the Germans, they were torn internally. Grand Admiral Raeder, head of the Kriegsmarine, believed that surface vessels posed the greater threat, whereas U-boat commander-in-chief Karl Dönitz thought that submarines would be most effective. This is still contentious territory because there is no doubt that great German ships such as the Bismarck had the capacity to cause significant damage. However, Dönitz argued that U-boats – properly resourced and in large enough numbers – would be much more effective in the tonnage war. If they could sink more tonnes of shipping than the Allies could build, it would result in victory for the Third Reich.

Was Dönitz right?

Yes, I think he was. At the start of the war he set a rather arbitrary requirement of 300 U-boats, yet he began with only 60 or so. When you consider that some of these would always be journeying to and from the battlefield, and some would be undergoing repairs, he often had only around 20 U-boats operational at any one time. However, the amount of damage that such a relatively small number of U-boats could inflict was quite astonishing – particularly when they operated in wolf packs from French ports after France had been neutralised. One of the most devastating attacks occurred in March 1943 when 22 ships from two convoys were sunk by a large group of U-boats.

It was at this point that the British Air Ministry was persuaded that very long range bombers – which had been theoretically available for nearly two years – could be deployed in the mid-Atlantic to cover what was known as the Atlantic gap. Within two months, the story of the battle had completely changed – and by May 1943 the campaign had been won.

So was the introduction of such bombers the crucial factor in Allied victory?

U-boats were more frightened of aeroplanes than anything else. Planes came out of the sky at high speed, forcing the U-boats to keep diving, meaning that they lost contact with the convoys. Prior to the introduction of the very long range bombers there was a large area in the mid-Atlantic that could not be reached from Iceland, Greenland, Northern Ireland, Scotland or the US by existing aircraft.

When these bombers first became available they were given to the Air Ministry which, in an extraordinarily dogmatic way, held on to them rather than making them available to the Admiralty. This contributed to a ferocious internal struggle between the two departments that one admiral likened to being more bitter than “our war against the Hun”.

Sir Arthur ‘Bomber’ Harris was convinced that the strategic bombing of Germany was the most effective way of bringing that country to heel, and that it was a waste to use aeroplanes to protect merchant convoys. Churchill invariably sided with Harris, until very late in the day, thus prolonging the Battle of the Atlantic by at least a year. As a result a great many ships were sunk and lives lost unnecessarily. Churchill was a great war leader but this was a great error, the greatest, in my view, of his entire leadership between 1940 and 1942.

When the Air Ministry finally consented, it took just 40 of the very long range bombers to transform the battle. So the introduction of the bombers was absolutely fundamental – but of course other things counted, including intelligence, weaponry, the skill of escort captains and the tactics they had begun to deploy to thwart U-boat attacks.

How important was the role of Bletchley Park?

In my view, not as important as people like to believe – especially if they watch movies! Of course, Enigma was broken thanks to Turing and his team. However, the naval Enigma was more complicated and better protected than the land version, and there were key periods where we couldn’t break it. The delays were quite considerable, despite the amazing efforts and skill within Bletchley. Between January and December 1942 there was nearly a year when we were not able to penetrate German codes at all; this was a big killing time, to use an unfortunate contemporary phrase.

Meanwhile, the German codebreaking system was getting into the British naval codes almost with impunity because of an underinvestment in security on our side. So at key points they were breaking our codes when we weren’t breaking theirs – and even when we were breaking their codes and diverting convoys accordingly, these orders to divert were being picked up by Dönitz, who was able to redirect the submarines. Enigma would then pick up on these redirections, and a kind of blind man’s buff went on. It was an extraordinary period.

What was life like for those who served in the battle?

In some ways it was just like the experience of war more generally: long hours and days of discomfort and boredom, punctuated by moments of extreme danger. It was a stressful experience and you had to be very resilient.

The weather played a big part in this. Sometimes ships would be sailing through appalling storms, unable to move. Slow, lumbering merchant vessels could not even make headway against the ferocity of these gales, and very often they would be driven back and unable to advance any distance at all. It could be extremely uncomfortable, very cold and very frightening. On the other hand, when the weather was lovely and skies were balmy you might think that all was well – but this was actually the most dangerous time, when it was easiest for the U-boats to attack.

There was often not much in the way of medical facilities. Nicholas Monsarrat, whose novel The Cruel Sea was set during the battle, joined the Royal Naval Volunteer Reserve and found himself a ship’s surgeon. He had never wielded a scalpel in anger nor given an injection, yet he found himself putting people’s eyes back in, stuffing their guts back into their stomachs. People were required to do things, while short of antibiotics – short of anything – to ease pain and suffering. Plus the food was dreadful, with not enough storage or fridge space.

Things were similar in the U-boats, which were extremely cramped and got very airless. If you were forced down by a ship or aeroplane depth charging, you would stay underwater until you were virtually asphyxiated by the lack of oxygen. You would be there waiting, waiting, waiting with the prospect of another depth charge descending from the surface. There would be the sound of creaking hulls and then, suddenly, massive explosions all around, leaving the whole U-boat shaking and shivering – or, very often, completely destroyed.

How much did people in Britain follow the battle?

People noticed when ships went down, but in general it was very under-reported. Churchill required significant censorship of the fact that U-boats were sinking British, Allied and neutral cargo ships. He was extremely worried about the paucity of good news – that very few U-boat crews were being captured compared with the huge Allied tonnage being lost month after month. There had to be some reporting of it, but it was often delayed and calculated to minimise the impact. This was compounded by the fact that the battle was being fought far away, out at sea, and that very few reporters were following the events. So in general the British public did not know a great deal about the sea war at the time.

What do you hope readers might take from the book?

I wanted my book to have an upstairs/downstairs quality, exploring the dramas at sea and in the capitals of the warring powers. I’ve sought to place the battle in the context of the wider war and I hope I’ve told the story in a way that brings it alive and makes people aware of just how vital these events were. The Atlantic was a lifeline – the carotid artery on which Britain depended. This was no motorway but a minefield, and it was a great mercy that the ships made it through.

Jonathan Dimbleby is a broadcaster, film-maker and historian who regularly presents BBC Radio 4’s Any Questions? His books include Destiny in the Desert: The Road to El Alamein (Profile, 2013).

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This article was first published in the Christmas 2015 issue of BBC History Magazine