Obtaining the United States as an ally was the major prize for the British in December 1917, since it brought significant potential naval resources that might win the war against Germany. American ships, notably older coal-burning destroyers sent to Queenstown soon after the American entry into the war, made a huge difference; by the end of August, there were 35 ships total. The formal unification of the British and American fleets on 7 December 1917 was coincidentally proceeded by a chance munitions explosion in Halifax, Canada, on 6 December 1917 (see Picture 4). Once Britain's main naval base in North America was destroyed, and there was no possibility of ever using America's ships against her, the unification of the two navies proceeded as planned the very next day.

The 6 December 1917 munitions explosion that destroyed Halifax was caused by an American-leased ship. One of the first large-scale humanitarian aid missions by sea occurred during World War I with the creation of the non-profit Commission for the Relief of Belgium (CRB). This aid organization distributed $927,681,485.08 worth of foodstuffs and clothing to Belgium and to German-occupied areas of Northern France. Because of the Commission's almost total reliance on international shipping, the CRB was once described by critics as a “piratical state organized for benevolence”: “Like a pirate state, the CRB flew its own flag, negotiated its own treaties, secured special passports, fixed prices, issued currency, and exercised a great deal of fiscal independence.”

The director, future U.S. president Herbert Hoover, had to obtain permission first from England and Germany to let the aid ships through the maritime blockade lines. From 1 November 1914 until the summer of 1919, over 900 CRB-leased ships successfully navigated not only the British naval blockade but also German minefields and swarms of U-boats conducting unrestricted submarine warfare. By delivering essential food aid, the CRB helped the British government focus the full impact of the starvation blockade against Germany rather than against helpless neutrals in Belgium and Northern France.

Hoover's efforts were supported by the U.S. government. But the British also had to cooperate fully if this aid program was to work. Inspections of the CRB ships took place at Halifax, Canada. Beginning in August 1917, inspections of the cargoes could also be carried out during the loading process in U.S. harbors.