He reported again to the Naval Academy as an instructor in the Department of Navigation between November 1, 1910, and June 10, 1912, a tour that included service as senior engineer officer of the battleship USS Iowa (BB-4) for the practice cruise of Summer 1911.

He reported to the Naval Training Station for duty in charge of a draft of men to Manila; then served as navigator of the armored cruiser USS Saratoga (ACR-2), operating with the Asiatic Fleet.

From June to November 1914, he commanded the distilling ship USS Rainbow (AS-7), which departed Manila Bay in July and surveyed the French Frigate Shoals, Hawaii, while en route to the Mare Island Naval Shipyard for decommissioning.

He was awarded the Navy Cross for "distinguished service ... as Naval Attaché ... in which capacity he had remarkable success in establishing and maintaining friendly relations with the Japanese authorities in supplying valuable information to the Office of Naval Intelligence and to the Commander in Chief of the Asiatic Fleet ... [and] with the purchase and building of ships in Japan for the United States Government.

"[5] Upon returning to the United States, Horne reported to the Office of Naval Intelligence in Washington, D.C., for a month of special duty.

[3] From March to June 1926, Horne was a member of the first class of captains persuaded by Bureau of Aeronautics chief William A. Moffett to undergo flight training at Naval Air Station Pensacola, Florida.

Horne qualified as a naval aviation observer along with most of the other captains in his class, which included future three- and four-star admirals Joseph M. Reeves, Harry E. Yarnell, Alfred Wilkinson Johnson, and Henry V.

[6] After serving as a member of the Naval Examining Board in the Navy Department, Horne temporarily relieved Captain Ernest J.

[6] As Wright's captain, Horne had additional duty as senior aide on the staff of Commander Aircraft Squadrons, Scouting Fleet.

He reported to the Fourteenth Naval District, Pearl Harbor on July 18, 1931, as chief of staff to the commandant, a position he held for two years.

[9] Promoted to the temporary rank of vice admiral, Horne served as Commander Aircraft, Battle Force (COMAIRBATFOR), from June 9, 1936, to January 29, 1938.

A year later, in the aftermath of the Japanese attack on Pearl Harbor, King was elevated to Commander in Chief, United States Fleet, and promptly forced Chief of Naval Operations Harold R. Stark to release his assistant, Rear Admiral Royal E. Ingersoll, to succeed King in command of the Atlantic Fleet.

COMINCH wielded supreme command over the operating forces of the Navy, while the CNO was responsible for their training and logistical support.

[15] During the war, Horne was actually de facto CNO, since King was preoccupied with his COMINCH and Joint Chiefs of Staff duties.

[16] Horne was also the officer responsible for budgets and financial management, the Navy's principal uniformed spokesman before Congress,[17] and a member—and later chairman—of the Army–Navy Petroleum Board from May 1943 to September 1945.

[17] Knox's campaign against King peaked in mid-January 1944, when a draft executive order threatened to separate fleet command from naval operations by making King a five-star "Admiral of the Navy and Commander, United States Fleets," while making Horne a four-star "Chief of Naval Logistics and Material" reporting directly to the Secretary of the Navy.

[20] However, on February 11, 1944, Congressman Carl Vinson, the chairman of the House Naval Affairs Committee, revoked his support for Knox's proposal.

Under the reorganization, which became effective on October 10, 1945, Edwards became VCNO while Horne was temporarily retained as a special assistant to the CNO so that he could handle demobilization and logistic rollback issues.

[21] Horne was placed on the retired list on August 1, 1946, but remained on active duty as special assistant and head of the Board of Review for Decorations and Medals until April 1947.

"I don't believe that the country will ever know the full contribution to the prosecution of the recent war by this quiet, modest, sincere, but tremendously effective and capable naval officer", said New York Congressman W. Sterling Cole.

[22] Truman Committee staffer John J. Tolan marveled, "In an entire lifetime, one is extremely fortunate to watch such men at work."

Horne had had no previous experience with logistics, and he tended to go by the old Navy tradition that you didn't get involved in what was happening in the engine room unless something went wrong, and then you brought a person up and bawled him out for it.

"[16] Horne was also an outspoken critic of the Nuremberg Trials, having stated: "As it has been my belief that the after-war emotional hysteria was responsible for the trial and imprisonment of the German high-ranking military and naval officers, and that we should reflect with shame upon our efforts for revenge upon men doing what we would do for our own country, I am glad to have my name included in any effort to atone for the injustice done to Admiral Doenitz and to any others who were likewise unfairly treated because they loved their country.