Protecting Allied Ships during WWI: The Convoy System Comes to Gibraltar

On August 17, 1917 the scout cruiser USS Birmingham arrived at Gibraltar with American Rear Adm. Henry B. Wilson aboard. His mission was to establish an American naval presence at Gibraltar, which is located at the southern tip of Spain less than 40 miles north of Morocco. Separated by the Strait of Gibraltar from Africa, this strategically important location is the entry point into the Mediterranean Sea. Allied forces understood that a strong naval presence in these waters could protect ships, and deter German U-boat attacks.

The straits proved a strategically critical center of Allied shipping. Supplies and troops from Asia and Australia sailed through the area on their way to France and Britain. Vital cargoes of food, raw materials, and troops from ports in Africa, South America and the Caribbean passed Gibraltar’s Atlantic side.  Seagoing cargoes for Italy came chiefly to Naples via Gibraltar and the western Mediterranean.

The Imperial German submarines raided Mediterranean and adjacent sea-lanes in the  unrestricted campaign of early 1917. Some of the most successful U-boat captains regularly patrolled the Sicilian Narrows south of Naples, the approaches to Marseille, the Southern coast of Spain, and down to Oran, Algeria. In the Atlantic, just beyond the Straits of Gibraltar, conditions were the same. In March of 1917 alone, 25 percent of merchant ships headed to Britain were sunk. This caused England’s grain reserve to drop to a six week supply. The Allies had to change their naval strategy to overcome aggressive German tactics.

On April 25, 1917, shortly after the United States officially joined the war, American Adm. W. S. Sims urged the British War Cabinet to adopt a convoy system—groups of ships moving together while being escorted by warships. He made the same appeal to the French government.  By May 1st the British government agreed to a trial convoy.  On the same day the U.S. Navy, anticipating a role in anti-submarine warfare, alerted 12 destroyers in New York and Boston to prepare to sail. On May 3rd the Navy reported a need for 36 destroyers and 100 smaller anti-submarine vessels for Europe. 

On May 10th the first convoy of the war sailed for Britain from Gibraltar. It arrived in England on the 22nd without loss and the Admiralty immediately mandated all ships bound for England arrive in convoy. In early June, the First Sea Lord Admiral John Jellicoe specifically requested more American anti-submarine ships for patrols around Europe. The U.S. Navy decided to establish “Base No. 9” at Gibraltar on July 5th. The next day Adm. Sims, and Adm. Jellicoe specifically requested seven gunboats and an armed American yacht for Gibraltar.  In response the U.S. Navy alerted 11 ships to prepare for “distant service” at Gibraltar under Rear Adm. Henry B. Wilson a week later. This force was augmented by six additional U.S. Coast Guard ships by the end of July.  Adm. Sims officially established this command under Adm. Wilson on August 1st.

The American vessels were placed on convoy duty almost as soon as they arrived.  They assumed control of nearly all the convoys between England and Gibraltar, coordinating with American coastal forces off France and Ireland.  Entering British home waters they turned over the convoy to the danger zone escort.  Ships from Base No. 9 met inbound Atlantic convoys at 10 degrees west of Gibraltar, or southwest of Lisbon and west of Gibraltar, to strengthen the escort.  At times coverage extended to 30 degrees west.  Outbound convoys to the Americas received the same coverage.  

Lighter units at Gibraltar formed patrols and convoy escorts in the confined waters of the straits. In their case they made aggressive patrols for submarines in all conditions, day and night. The crews suffered in rough conditions in the small ships.

Within the Mediterranean, U.S. Navy ships escorted local convoys, American supply convoys and military support landing in Marseilles, Italian ports, and the Balkan front at Salonika. Americans escorted French convoys between France and their North African colonies. Most other traffic across the Mediterranean was escorted by British and other allied escort ships based on Malta.

Adm. Sims and Secretary of the Navy Josephus Daniels both wrote that Gibraltar was the gateway for more maritime traffic than any other port in the world. He estimated that approximately one quarter of all Allied merchant, supply, and troopship voyages passed through Gibraltar. The American force at Gibraltar would swell to 41 ships, including at least one maintenance ship. Almost 5,000 naval officers and men served at Base No. 9 at Gibraltar during World War I. This strategically important station competed for importance with the routes bringing troops into France and England. It was a focus of enemy submarine attacks up to the last days of the war. It is no coincidence that the first escorted convoy sailed from here, and no surprise that the U.S. Navy took such an important role in convoy duties through 1918.

 The threat of unrestricted submarine warfare was met by American insistence on a strategy of escorted convoys backed by the commitment of many ships to the ensuing campaign.  The American escorts from Gibraltar alone escorted 10,478 voyages.  There is an American Naval Monument at Gibraltar to commemorate their efforts.

Learn more about the ABMC Naval Monument at Gibraltar.

Suggested Reading

Josephus Daniels, Our Navy at War (Washington, Pictorial Bureau, 1922)  

William Sims, The Victory at Sea (New York, Doubleday, Page and Co., 1920)

Henry B. Wilson, An Account of the Operations of the American Navy in France during the War With Germany (  Navy Department, 1919)  

Frank A. Blazich Jr., United States Navy and World War I: 1914–1922, (An annotated timeline) Naval History and Heritage Command