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Forgotten Wrecks of the First World War

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Part 4: Breaking the Blockade

The submarine was a comparatively new weapon and yet to prove itself in war. Neither the British nor the Germans had particularly great expectations of them when war broke out – it was thought they may be useful scouts for the fleets or as patrol vessels, but not as a major instrument of war.

That changed in September 1914. The German Imperial Navy demonstrated the potential of new technology when one U-boat (U-9) sank three British cruisers (Hogue, Abukir and Cressy) in just over an hour. The Royal Navy, caught on the back foot, was unprepared for this new form of warfare. Whilst their fleet dispersed to the west side of Scotland whilst Scapa was suitably defended, Germany quietly began building more U-boats for the coming years.

Germany first tried to conduct a commerce war on British merchant shipping in 1915. In contrast to the later campaign, this was not intended to completely destroy British merchant traffic. Rather, the aim was to put pressure on the British government to lift its own blockade which, it was believed, would take six weeks. In February of that year, the waters around Britain were declared a war zone in which any enemy merchant ship was liable to be attacked. This was a restricted campaign to damage Britain’s merchant trade, but was not meant as a terror attack on civilians. The crews of the vessels attacked were to be given sufficient warning and time to abandon ship and reach safety, according to the rules of war and the Declaration of London.

The larger U-boat fleets prowled around the North Sea and English Channel shipping lanes. Both the Mercantile Marine and the Royal Navy were unprepared for this form of warfare and could do little to interfere with the U-boats unless they caught them on the surface. But the campaign was not without problems. The sinking of the Lusitania and the Arabic liners, coupled with other attacks that breached the rules of war, brought intense political pressure on Germany from other nations, particularly the United States which was still neutral. In August the campaign was abandoned, having already failed to force Britain to lift its blockade in six weeks.

By 1916, Germany came to realise that the U-boat was still the best weapon to fight the blockade.  In March a new restricted campaign was begun and once more flotillas of submarines patrolled around Britain’s coast.[i] Once again merchant ships losses increased, but again the over enthusiastic actions of some U-boat captains created political pressure on Germany. As the passenger ship Sussex crossed from Folkestone to Dieppe in March, she was torpedoed without warning by U-29. Although the ship didn’t sink, over 50 men, women and children were killed in the explosion. The outrage in the United States forced Germany to issue the Sussex Pledge, a promise not to attack passenger ships or merchant ships without armaments at all, and that any civilian vessel that was attacked must be given time for the crew to escape. The pledge essentially ended the 1916 campaign in May.

The German admiralty faced a dilemma by the end of the year. Increasing number of merchant ships were being armed for their own protection, but this made it dangerous for a U-boat to surface and warn the crew to abandon ship before attacking. In any event, surfacing before an attack negated the major advantage of a submarine – the ability to surprise its enemy. These factors, along with the failure to break the British blockade with the previous campaigns or at Jutland led to a new strategy being approved in 1917.

Proponents of U-boat warfare believed that, with sufficient numbers of submarines available, a sustained campaign against merchant shipping could destroy the British Mercantile Marine in six months. Such a blow would create an untenable situation in Britain, which relied on maritime trade in order to survive.[ii] Such a campaign would need to have a no holds-barred approach; political considerations would need to be ignored but, it was hoped, would be rendered irrelevant by the speed of Britain’s downfall and eventual capitulation.

Accordingly, on the 1st February 1917, a wider expanse of sea around Britain was declared a war zone within which any vessel, military, civilian, belligerent or neutral, was at risk of attack without warning. Only two days later the United States severed all diplomatic relations with Germany. In April, in response to the campaign and the infamous Zimmerman Telegram (a diplomatic entreaty from Germany to Mexico pledging to support them in the event of a war with the States), the United States declared war.

The race was now on to destroy British merchant shipping faster than the Allies could build it and before the British blockade completely starved Germany. Admiral Beatty commented that "The real crux lies in whether we blockade the enemy to his knees, or whether he does the same to us."

Merchant ship losses increased dramatically, particularly in the seas around Britain. For a while it looked like the campaign may work; losses quickly outstripped the building programme and led the First Sea Lord Admiral Jellicoe to warn that Britain could not pursue the war into 1918 unless the situation was improved.

The eventual victory over the U-boat was owed to several factors but some were more important than others. For years the Royal Navy had been improving its anti-U-boat weapons and now the depth charge had become a proficient weapon. The entry of the United States into the war opened up a wealth of industrial power that enabled a sustained shipbuilding programme to be maintained and brought numerous warships into home waters. But perhaps the most important factor was the use of convoys.

Although it may seem obvious in the light of the Second World War that convoys enabled merchant ships to be better protected, that was not the opinion of the Admiralty in the First World War. From 1914 to 1917, merchant ships had sailed the routes and timetables they had always done; the only nod to the war being the extinguishing of lights, the fitting of a deck gun and perhaps the occasional escort. The idea of gathering ships into convoys seemed to play into the hands of the U-boats; enabling them to sink a collection of vessels all neatly lined up for their torpedoes. In fact the opposite was true. A scattering of a hundred ships bustling around the English Channel would mean that a U-boat was bound to stumble over a target sooner or later. But if those 100 ships were gathered into five convoys, then the U-boat would be far less likely to encounter one. Twenty ships in close company are no easier to spot at sea than two; reducing the number of isolated ships crossing the channel reduced the chances of them being found.

Grouping vessels in a convoy also made it easier to defend them. A few Royal Navy warships could protect dozens of vessels in this way and the results quickly spoke for themselves. Rear Admiral William Jameson observed that “About one in every ten ships sailing alone was sunk; for ships in convoy it was between one and two in a hundred.”[iii]

Losses steadily fell into 1918 and, although the campaign continued until the end of the war, it had shot its bolt: the U-boats steadily became less and less effective. At the same time, the Allied blockade was making more of an impact as time passed. Starved of imports and slowly running out of the supplies needed to grow its own resources, the German population was slowly starving and the armed forces were running out of war materials. Successes on the Western Front pushed the enemy back towards the German border, but the Royal Navy had constantly been squeezing Germany since 1914.

One only needs to look at the seabed to see the true cost of the war at sea. Around the shores of Britain and Ireland lie the remains of some 5,000 vessels sunk between 1914 and 1918. Along the south coast of England alone lie 1,100 ships. The vast majority are British merchant ships lost in this incredibly important strategic race between Germany and Britain.

Return to Part 3


[i] It should be noted that attacks on merchant ships (theoretically in accordance with the rules of war) still occurred between these campaigns as and when patrolling submarines came across them. The campaigns represent periods of increased activity and greater numbers of U-boats at sea with a set mission to target merchant shipping.

[ii] Even today, 95% of Britain’s imports come by sea.

[iii] Rear Admiral William Jameson (1965) The Most Formidable Thing. Rupert Hart-Davis, London.