In November 1914 he reported to the Mare Island Naval Shipyard where the new submarine USS F-1 was being fitted out, and served as her commander from June 1917 until she was lost on 17 December 1917.

He served as its commander from June 1917 until 17 December 1917,[1] when F-1 collided with her sister ship USS F-3 during maneuvers, and sank within seconds with the loss of nineteen of her crew.

[4] Montgomery was then assigned to the submarine USS R-20, which was being fitted out at the Union Iron Works in San Francisco.

[1] Following the usual pattern of alternating sea and shore duty, he commanded the Naval Air Station Seattle from August 1930 to May 1932.

[2] From July 1932 until May 1933 he was an aviation officer on the Staff of Commander Cruisers, Scouting Force, on its flagship, USS Chicago.

[2] Montgomery served as head of the Flight Division in the Bureau of Aeronautics in the Navy Department from July 1939 until June 1940, when he assumed command of Ranger.

He was serving in this post when the United States entered World War II after the bombing of Pearl Harbor in December 1941.

[5] During the Gilbert and Marshall Islands campaign he led Task Group 50.3, with the carriers Essex, Bunker Hill and Independence.

[7] For his part in the campaign, he was awarded the Navy Distinguished Service Medal:As Commander of a Carrier Task Group in action against enemy Japanese forces in the Central and South Pacific Areas from November 18 to December 10, 1943 ... (He) directed the operations of his Task Group in repeated aerial attacks against Tarawa, Gilbert Islands, through the preparatory periods and in support of the subsequent landings, greatly assisting our forces in the successful occupation of this strategic island ... carried out numerous vital air raids on Japanese shipping, aircraft and installations on Kwajalein Atoll, Marshall Islands, despite a persistent hostile night attack lasting five hours ... and previous operations against Rabaul, New Britain, and Wake Island, contributed in large measure to our ultimate victories in the Pacific Areas ...[1] For a raid on Saipan, Montgomery was award the Navy Cross: For extraordinary heroism as Officer in Tactical Command of a Carrier Task Group, in action ... in the vicinity of Saipan, February 12, 1944.

With his task group subjected to repeated attacks by enemy torpedo and bomber planes, (he) ... skillfully and successfully directed their gunfire and combat air patrols in destroying seventeen hostile planes ... delivered damaging attacks against enemy shipping, aircraft and shore installations and ... also obtained valuable photographs.

[9] Montgomery was awarded a second Navy Distinguished Service Medal for his part:as commander of a Task Group of Carriers and screening vessels in operations against the Japanese forces from March through June 1944.

In attacks on Palau ... Marcus and Wake ... the aircraft under his command inflicted great damage on enemy shipping and shore installations.

After effectively organizing and expeditiously developing the forces of his command (he) ably directed his group in highly successful concentrated operations against the enemy, inflicting severe and costly damage on the aircraft, shipping and shore installations at Leyte, Manila and Luzon.

By his superb professional skill in all the phases of aerial warfare and his capable leadership, he inspired the men of his command to maximum effort throughout this critical period and contributed to the sustained prosecution of the war in this vital theater ...[1]Montgomery became Commander Fleet Air, West Coast, with his headquarters at the Naval Air Station, San Diego, in January 1945.

[5][2] He reverted to his permanent rank of rear admiral in August 1947, and became commander of the Alaskan Sea Frontier and the 17th Naval District.