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Commerce Raiding in the Irish Sea

Cian Lynch | University College Cork

During the First World War, roughly 5,000 merchant vessels were sunk; roughly 1,800 of these in Irish waters. In a final grand strategic gamble, Germany unleashed its fleet of U-boats upon the waters of Great Britain and Ireland to literally starve Britain out of the war. Ireland, then an integral part of the United Kingdom, served as a crucial source of foodstuffs and raw materials for Britain to sustain its war effort and so naturally became a target for the German Navy. 

At the outbreak of war, Britain was the largest maritime power the world had ever seen, though it had a crucial weakness; as a heavily industrialised nation, and an island at that, Britain was reliant on imports to sustain its populace and economy. Of most immediate concern was its reliance on imported food; two-thirds of Britain’s food originated abroad and eighty per cent of its key foodstuff, cereals. Lacking sufficient agricultural production or significant reserves of food or raw materials, Britain was an opportune target for a blockade.  

A German-language map of the world. Great Britain appears as an Octopus pulling all the world towards it.
The German perspective of British trade reaching all corners of the globe and pulling resources towards Britain. The caption reads “Freedom of the seas.” Image source: P.J. Mode collection of persuasive cartography, #8548. Division of Rare and Manuscript Collections, Cornell University Library.

In response to the Royal Navy’s successful blockade of Germany, the Imperial German Navy sought to retaliate in 1915. The High Seas Fleet of the German navy could not defeat Britain’s Grand Fleet in open battle, so instead Germany turned to a campaign of commerce raiding to force Britain out of the war; its fleet of submarines was unleashed upon shipping in British waters without due regard for the safety of the crews or cargo aboard. In an even more obscene violation of maritime law, even the vessels of neutral nations could be targeted by U-boat commanders within these waters.

This would be part of a campaign of unrestricted submarine warfare. Put simply, the commanders of Germany’s fleet of submarines would not be required to follow international law within defined warzones in the waters of Entente nations, namely the United Kingdom, France, Italy, Russia, and later the United States of America. Ships could be torpedoed without warning, mines could await unlucky victims off every headland and at the mouth of every harbour, and worst of all, no effort would often be made to rescue survivors who would be left to perish in the icy waters of the North Atlantic. 

Part of a recruiting poster showing drowning women and children in the wake of the RMS Lusitania disaster. 1,198 people would perish in this incident. Image source: Hampton Sides, ‘Erik Larson’s ‘Dead Wake,’ About the Lusitania’, The New York Times. 5 March 2015.

Naturally, the barbaric nature of this campaign would be offensive to the sensibilities of all nations, but most crucially to the neutral United States. In order to balance the desire to crush British shipping with the strategic necessity of keeping the US out of the war, the initial campaign of commerce raiding lasted only eight months. This brief reprieve would not last long; from 1917 until the war’s end, Germany would launch a renewed campaign of submarine warfare, with the desire to force Britain out of the war before the US could come to its aid. 

The principal weapon of this campaign of commerce raiding would be the U-boat, a precursor to modern attack submarines. More than 300 of these terrifying weapons would be employed against generally slow, unarmoured, and typically unarmed merchant vessels. These sleek weapons of war could employ torpedoes, mines, deck guns, and bombs to wreak havoc on unsuspecting merchantmen. Capable of long periods of endurance at sea, by the middle of the war these submarines could reach the shores of America, but at any point in the war could engage vessels in the Irish Sea. 

An illustration of a U-Boat on a dark and stormy night.
SM U-9, a pre-war era U-boat that served with distinction during WWI. Image source; United States National WWI Museum and Memorial.

As an example of their destructive potential, SM U-9 (pictured above) destroyed three Royal Navy ships in one hour with only four torpedoes. This engagement would kill 1,459 British sailors. Four U-boats had the distinction of sinking over one hundred merchant vessels each, with SM U-35 sinking over 200 merchant vessels alone. To these capable killing machines, the well-plied waters of the Irish Sea became an opportune hunting ground, known to their crews colloquially as “torpedo alley.”   

Ireland exported some key resources vital to the British war effort, such as iron ore, manufacturing chemicals, and medicines, but of far greater importance was the immense supply of foodstuffs that Ireland exported to Britain. After the United States, the second greatest exporter of food to Great Britain was Ireland. Almost one million cattle were exported from Ireland to Britain in 1917 alone, as well as 400,000 sheep, 350,000 lambs, 110,000 tons of potatoes, and much more. Without this sustenance, the situation could have become very dire; at the pinnacle of the submarine campaign in April 1917, Britain’s supply of wheat, its principal foodstuff, had dwindled to just six weeks. The situation would become so desperate as to necessitate the rationing of key foodstuffs such as bread, butter, meat, and sugar in 1917. At a time when the success or failure of the British war effort hung in the balance of whether its populace could be physically sustained, Ireland’s importance as a supplier of foodstuffs cannot be overstated.  

Propaganda poster from WW1 of a loaf of bread with ships in the background. The text reads Save the Wheat and Help the Fleet: EAT LESS BREAD
British propaganda poster encouraging citizens to eat less bread to ease the burden on British shipping. Image source: Imperial War Museum

At the height of the war, a merchant vessel was being sunk every two days in these waters. With each vessel sunk, Britain would lose more of the vital resources it needed to sustain its war effort. In just three days in 1915, seven thousand tons of wheat was sunk while en route to Britain, an amount sufficient to feed 60,000 people for a year. The destruction of Britain’s ability to import food was a stated aim of Germany’s campaign of commerce raiding. In Chief of the German Naval Staff von Holtzendorff’s letter to the Chief of the Army General Staff he outlined his view of unrestructured submarine warfare as the “only means” to bring about a German victory in WWI.  

While Britain would thankfully never reach the point of starvation, or even see the sharp decline in nutritional value as experienced in Germany, the situation did become so dire as to worry the British cabinet and Admiralty about the likelihood of being forced from the war. To demonstrate how close to the brink of defeat Britain came, the German Admiralty estimated that it needed to sink 600,000 Gross Register Tonnes of shipping per month to compel Britain to seek peace terms. In April of 1917, U-boats would sink almost 150% of that figure and sink over 6,000,000 GRT of shipping that year alone.  

Less abstract than these figures were the thousands of sailors and passengers that never made it back to shore. Some were lucky, like Captain Patrick F. Kelly of the City of Cork Steam Packet company who would narrowly escape death twice while commanding SS Bandon and later SS Inniscarra, both lost to U-boat warfare. Others would not have such fortune, like Frances Saunders of Kingstown, now Dún Laoghaire, who would lose her life in the sinking of RMS Leinster having previously been widowed by the 1895 Kingstown Lifeboat Disaster.  


Ireland too was heavily impacted by the destruction of shipping; As Britain became increasingly cut off from other sources of foodstuffs, the more it came to rely on Ireland. Food became scarce in Ireland, with fears of famine igniting by the end of the war. The loss of coal imports from Britain, such as on the SS Etal Manor which sank outside of Cork carrying 2,550 tons, meant that homes were cold, dark, and lacked cooking fuel. Irish shipping companies were irreparably damaged, with the City of Cork Steam Packet Co. losing six of its eight vessels, and many folded after the war. Hundreds of lives were lost in Irish waters on steamers such as RMS Leinster, SS Laurentic, and, most famously, RMS Lusitania. The loss of so many ships, crews, and livelihoods would immensely damage the vital economic link between Ireland and Britain.

An illustrated propaganda poster of a young sailor. The caption reads DO YOUR BIT: SAVE FOOD.
British propaganda poster encouraging citizens to eat less food to decrease the necessity for international shipping. Image source: Imperial War Museum

Britain sought to combat the campaign of commerce raiding through a two-pronged approach; the first was to decrease reliance on foreign suppliers by increasing domestic production, and the second was to mitigate and defeat the campaign of commerce raiding.

In order to decrease its reliance on imports, a campaign by the newly established Ministry of Food sought to increase the amount of food grown within Great Britan and Ireland. From 1916 to 1917, 975,000 additional acres of tillage became available, massively increasing the amount of food that could be produced in Britain and Ireland. Two-thirds of this additional acreage was in Ireland, further highlighting its contribution to sustaining the British war effort.

In terms of diminishing the losses of shipping, greater efforts were made to protect shipping and to combat U-boats operating in British and Irish waters. These methods proved immensely effective; whereas one merchant vessel was lost every two days in 1917, this figure was reduced to one every two weeks by the summer of 1918. The most effective method of protecting shipping in the Irish Sea was the advent of convoys; by grouping merchant vessels in convoys protected by destroyers and submarine chasers, merchant vessels were made both more elusive targets for U-boats and far more difficult to destroy. U-boat commanders could no longer simply lie in wait off of strategic headlands and await their prey lest they be destroyed in turn. Furthermore, the additional protection made it necessary to strike from further distances with torpedoes, greatly reducing their accuracy.

A grainy photograph of a fleet of boats.
A transatlantic convoy originating from the US. Image source: US Naval History and Heritage Command.

Other factors that increased the ability of the Royal Navy and US Navy to protect shipping were the use of minesweepers to clear sea lanes of threats, seaplanes to patrol waters ahead of convoys, lighter-than-air dirigibles to increase the operational awareness and effectiveness of convoying naval vessels, and naval intelligence to divert and halt threatened convoys. On board the merchant vessels themselves, the use of defensive armament, the advent and use of dazzle camouflage to disrupt the ability of U-boats to strike their targets and sailing in a zig-zag pattern all helped to decrease the likelihood of being torpedoed.  

A German-language map of the waters around the British isles. Black dots represent vessels sunk - there are very many black dots.
Vessels claimed to have been destroyed by the German U-boat fleet in 12 months. Image source: P.J. Mode collection of persuasive cartography, #8548. Division of Rare and Manuscript Collections, Cornell University Library.

After the war, David Lloyd George would remark in his memoirs “The food question ultimately decided the issue of this war… What is the explanation of so obtuse, and general a neglect of this vital war front?” Given Ireland’s importance as a supplier of foodstuffs to Britain at a time when Britain was in desperate need, one must ask why greater attention has not been paid to the contributions of Ireland to the British war effort. As demonstrated, shipping in the Irish Sea was immensely impacted by commerce raiding in the Great War, though efforts by the Royal Navy and US Navy to protect merchant shipping were effective.  


Further reading: 

  • Roy Stokes, U-boat alley: The U-Boat War in the Irish Channel during World War I (Compuwreck, 2004).

  • Hew Strachan, The First World War (Simon and Schuster, 2006). 

  • Paul G Halpern, A Naval History of World War I (Naval Institute Press, 2012). 

  • Karl Brady et al., Warships, U-Boats & Liners (Irish Stationery Office, 2012). 

  • Niamh Gallagher, Ireland and the Great War: A Social And Political History (Bloomsbury Academic, 2020). 


Cian Lynch is a PhD student in University College Cork’s School of History. His current area of research is commerce raiding in the First World War, but he has an interest in contemporary defence and security, International Relations, and maritime history more generally. Cian currently serves as a corporal in the Irish Army Reserve. 


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