The influence of Mahan led to expectations - some accurate, some to be disappointed - about America's next major military involvement. Mahan's ideas seemed to work in the Spanish-American War, but by 1917, technology had changed, and the war in question had a different geographic configuration. Historians Allan Millett and Peter Maslowski note that
during the green April of 1917, as America entered "The Great War," a United States senator cornered a General Staff officer and asked the critical strategic question of the intervention: "Good Lord! You're not going to send soldiers over there, are you?" Some eighteen months later, the answer was clear as the American Expeditionary Force of over 2 million men, cooperating with the armies of France and the British Empire, bludgeoned Imperial Germany into an armistice. Supporting the AEF stood a Navy and Marine Corps of over 600,000. In the United States and in places as far separated as northern Italy, polar Russia, and Siberia, another 2 million American soldiers served the war effort and diplomacy of the Wilson administration. World War I was the debut of the United States as an international military power. Like most debuts, the war brought its share of high anticipation, major disappointment, dogged accomplishment, and exaggerated exhilaration.
Admiral William Sowden Sims was building his career as a naval officer in the years before WWI, in the same years during which Mahan's views were influential. Mahan had not foreseen the importance of the submarine, and the importance of convoys and the other defensive measures which would become important in an era in which the submarine gained much significance. Mahan's hypotheses about naval warfare were centered around the concept of decisive battles. In WWI, convoy duty and submarine hunting would be important as well. Given the international prevalence of Mahan's ideas, a defensive tactic taken by some navies was simply to refuse to be engaged in a 'decisive battle.'
Admiral Sims, commanding U.S. naval forces from his station in England during WWI, had to create new concepts about naval warfare to fit the new circumstances. Working with his English counterparts, he was able to develop effective anti-submarine tactics. This can be interpreted variously as moving past Mahan's views, or as simply updating Mahan's hypotheses. Historian Russell Weigley writes:
By the time the United States entered the World War in April, 1917, the intermediate objective of command of the sea had in a conventional sense been achieved. The Royal Navy had the German High Seas Fleet securely bottled up in German coastal waters. Unfortunately, when the United States entered the war the German submarine campaign was making conventional command of the sea appear a very bad joke. William S. Sims, now a rear admiral, arrived in London soon after the American declaration of war to learn from the Admiralty's statistics that Great Britain was within measurable distance of strangulation. The submarines were sinking one ship of every four that left England, and the British were able to replace only one ship in ten. With the submarine and the self-propelled torpedo employed against a vulnerable maritime nation, the guerre de course, the commerce-raiding war, was becoming an immense German success, Mahan to the contrary notwithstanding. Indeed, one of the principal mistakes the Germans had made was to have paid too much heed to Mahan and to have built too many battleships and not enough submarines before the war.
In any case, WWI did not occur as Mahan thought it might, first because armed conflict on land was more than significant and did not leave the matter to be settled at sea, and second because the naval fighting did not center around one or more decisive battles, but rather around convoy duty and submarine warfare. Mahan died in 1914 and did not live to see WWI. Admiral Sims commanded those U.S. naval forces which operated from England during the entire American involvement in WWI. He is considered to be an excellent naval officer, and he authored a book about the naval aspects of WWI; his work is still honored by the U.S. Navy.