U-Boats in the Irish Sea, 1917-18

On 1 February 1917, the German navy began an unrestricted U-boat campaign of attack on sight and without warning that focused on the shipping in Irish waters.


Throughout the First World War, the UK imported significant amounts of food from the United States, Canada and through Gibraltar. The German naval command calculated that they could starve Britain into surrender and win the war with a five-month campaign against merchant shipping. The first few months were outstandingly successful. Germany had anticipated the US declaration of war on 6 April 1917, but they believed they could defeat the British before the US could intervene.

Incoming merchant ships sailed alone and large numbers were sunk on the south-western approaches to County Cork. The new Prime Minister, David Lloyd George, was quickly convinced that escorted merchant convoys were the answer to the problem and by the end of April, he had persuaded a reluctant Admiralty to agree. Incoming convoys were provided with British and United States destroyers as escorts. The U-boats had difficulties even finding the convoys and losses reduced significantly. Outgoing shipping continued to suffer for a time until they were convoyed, too.

In autumn 1917, the U-boats extended their attacks into coastal waters where ships were generally sailing alone. In the Irish Sea, they sank Irish and British owned ships regularly into the spring of 1918. Here the Admiralty still generally relied on anti-submarine patrols despite the mounting losses and persistent lobbying by Irish politicians and the City of Dublin Steam Packet Co (CoDSPCo) to provide escorts for Irish ships.

In contrast, Milford Haven did develop small coastal convoys successfully. The local command here may have been more convoy-orientated because Milford Haven became an important assembly port for outgoing ocean convoys.

‘It is fatal to send out ships on the assumption that local patrols can protect them.’
Milford Haven commander, Vice Admiral Charles Dare, October 1917.

The Admiralty seem to have been slow in their acceptance of convoy. It appears they believed that amateur strategists like Lloyd George and Hankey were pushing professionals (them) to take responsibility for a huge difficult task which might not succeed.

Historian Jan Breemer puts it well:

‘It took the circumvention of the navy’s formal hierarchy by a relatively junior officers to make the political leadership aware that the navy’s rejection of the convoy system had been based, in good part, on an inflated estimate of the magnitude of the job.’

Ultimately, the Admiralty hierarchy recognised that their own survival was at stake and supported convoys. Many remained unreconstructed supporters of ‘aggressive’ patrolling rather than ‘passive’ convoying.