In addition to air raids, Germany initiated a submarine campaign that attempted to cut off and disrupt Allied trade routes. German submarines, known as U-boats, were armed with torpedoes and mines. Their tactics were successful and by 1917 there were widespread food shortages, with rationing being introduced in 1918. As a gesture of solidarity, King George V and Queen Mary also adopted rationing in the Royal Household. In addition, when the court was in residence at Windsor Castle the Queen was recorded spending several hours a day planting potatoes at Frogmore on the Windsor estate.

The most important Allied counter to the U-boat threat was the use of convoys. These were merchant ships grouped together and accompanied by warships. A significant naval success came on 23 April 1918, when British naval forces attacked Ostend and Zeebrugge, ports used by the Germans as submarine bases. Throughout the war, pieces of sunken German submarines were recovered by Royal Navy divers. Their salvage missions were important as they sometimes led to the retrieval of useful military intelligence and new technological innovations.