Understanding the crucial importance of the war at sea, sometime early in the autumn of 1917, Beston contacted Ellery Sedgwick, the editor of The Atlantic Monthly, inquiring whether the magazine might be interested in a series of articles on the United States Navy. Sedgwick expressed interest and wrote a letter of support for him that read in part, “Mr. Henry Sheahan, a valued contributor to The Atlantic, who has made excellent use of his opportunities for writing on the French front and elsewhere, now desires the privilege of gathering material for stories taken from the Naval Service of the United States…Mr. Sheahan has, in his relations with this magazine, always proved himself discreet and reliable, and we hope that his present efforts may meet with help and success." Beston then wrote to the Secretary of the Navy, Josephus Daniels, asking the Secretary for permission to cover the operations of the Atlantic fleet in its efforts against the German U-boats. Secretary Daniels agreed and wrote a letter to Admiral Sims recommending that Beston be permitted to report on the Navy’s operations for The Atlantic.
Beston reached Scapa Flow in April 1918 he was assigned to the New York. The ship’s chaplain, a Methodist minister named J. Luther Neff, who was to become a lifelong friend of Beston’s, later recalled how they first met: "In April Henry Beston Sheahan, a correspondent with the Atlantic Monthly press, joined our ship on his round of the Naval Bases in European waters. Admiral Rodman, who didn’t particularly care for ‘writer fellers,’ asked me to be Sheahan’s host while he was aboard. Fortunately, in this period, the Fleet put to sea—a most impressive sight and experience—and we steamed the old Viking route eastward to Norway and the mouth of the Baltic Sea. Henry and I became good friends during those days together in the North Sea, and the stimulating talk sessions in my cabin in the evenings."
For the next four months Beston traveled with the fleet, writing articles for The Atlantic and for other periodicals such as the North American Review and The Outlook. Despite Admiral Rodman’s suspicion of “writer fellers,” Beston was received warmly by the crews he stayed with during his time with the fleet, and struck up lasting friendships with a number of the men, including Reverend Neff and several of his comrades on board the USS New York. Much of Beston’s time was spent with the American destroyers and sub chasers, but he also had an opportunity to visit the aviators at a naval air base in southern England, talk to men whose ships had been torpedoed, and interview an enormous variety of specialists within the fleet—marines, signalmen, and members of the merchant fleet and the armed guard. Beston was particularly fascinated by the American submarine fleet, and when he was invited to come along with one of the submarine crews on a training mission he was enthralled by the experience, writing “there is no more thrilling game in the world than the game of periscope vs. periscope.”
As was the case with A Volunteer Poilu, the descriptive talent that is one of the hallmarks of Beston’s writing in later works such as The Outermost House is again evident in Full Speed Ahead. One such example is in the chapter entitled “The End of a Submarine,” where he describes a submarine hunt that he witnessed while aboard an American destroyer. The destroyer was moving into position to escort a convoy when a U-boat’s periscope was spotted about three hundred yards away. The general quarters alarm was sounded and the ship raced toward the submarine. The destroyer then “began a beautiful manœuvre,” writes Beston, placing a buoy near the place where the submarine had last been spotted before submerging, then dropping a series of depth charges along the projected path of the U-boat. For several hours, nothing more was seen of the submarine, until a report came in from another destroyer that signs of oil coming to the surface had been spotted. When Beston’s destroyer returned to the scene of the morning’s battle, he saw: "a great area defiled by the bodies of fish, purple T.N.T. dust and various bits of muddy wreckage which the explosions had shaken free from the ooze. Gulls, already attracted to the spot, were circling about uttering hoarse cries. In the heart of this disturbed area lay a great still pool of shining water and into this pool, from somewhere in the depths, huge bubbles of molasses-brown oil were rising. Reaching the surface, these bubbles spread into filmy pan cakes round whose edges little waves curled and broke."
Vivid and straightforward, the understated description evokes an eerie, chilling sense of the terrible events that must have transpired under the waves.