Roosevelt enlisted in the United States Army Air Corps in 1940. He served as a pilot and unit commander in the United States Army Air Forces (USAAF) during World War II.
In January 1943, Roosevelt accompanied FDR as a military attaché to the Casablanca meeting and the subsequent Cairo and Tehran Conferences. At the Tehran Conference, Elliot Roosevelt, apparently under the influence of alcohol, sided with his father in approving of large-scale executions of German POWs by the Soviets..
Roosevelt commanded the following units:
- 3d Reconnaissance Group, 11 July—13 August 1942 at the rank of major; 30 September 1942—1 March 1943 ending at the rank of colonel
- Assigned to Twelfth Air Force and flew P-38 Lightning (F-5) photographic reconnaissance missions during the North Africa campaign in Algeria and Tunisia
- 90th Reconnaissance Wing, 22 November 1943—25 January 1944 at the rank of colonel
- Assigned to Twelfth Air Force, command and control organization that provided photographic reconnaissance to both Twelfth and Fifteenth Air Forces. Operationally controlled both 3d and 5th Reconnaissance Groups in Tunisia. The 90th's subordinate units reconnoitered airdromes, roads, marshaling yards, and harbors in Italy after the Allied landings at Salerno.
- 325th Reconnaissance Wing, 9 August 1944—17 January 1945 at the rank of colonel; 22 January—13 April 1945 ending at the rank of brigadier general
- Assigned to Eighth Air Force, command and control organization that through subordinate units, flew reconnaissance over the waters adjacent to the British Isles and the European continent to obtain meteorological data. Wing aircraft collected weather information needed in planning operations; flew night photographic missions to detect enemy activity; and provided daylight photographic and mapping missions. The wing also flew photographic missions over the Netherlands in support of Operation Market Garden in September 1944 and operated closely with tactical units in the Battle of the Bulge (December 1944—February 1945).
Roosevelt flew 300 combat missions. His decorations included the Distinguished Flying Cross. As a chase pilot for the Operation Aphrodite flights in 1944, he witnessed the death of Joseph P. Kennedy, Jr. over Blythburgh, England.
Warplanes purchasing scandal
In August 1943, Colonel Roosevelt was asked by General of the Army Air Forces Henry H. "Hap" Arnold to select among several potential photo reconnaissance aircraft under development to determine a successor to the high-flying and fast camera carriers then in use, though the reason for Arnold's choice of Roosevelt was not made public. Roosevelt assembled a group of five air officers including veteran RAF reconnaissance pilot Flight Lieutenant D. W. Stevenson. Upon their arrival in Los Angeles Roosevelt and his group were met by eight limousines arranged by John W. Meyer, a publicist and former nightclub owner who was employed by Hughes Aircraft. On his first day in town, Roosevelt was taken by Meyer to the Hollywood film studio of Warner Bros. and introduced to Faye Emerson, an actress with whom Roosevelt was soon linked romantically. Over the next three days, Roosevelt and his group were seen with Meyer in Hollywood nightclubs and at parties in luxurious mansions in the company of aspiring actresses paid $100—400 per night by Meyer, the higher figure equivalent to $}} in current value. On August 11, Howard Hughes showed the group his Culver City operation, then personally flew them to see the Hughes D-2, an experimental twin-engine, wooden reconnaissance aircraft being assembled at a Hughes facility in the Mojave Desert. The aircraft had already been turned down ten months earlier by Chief of Army Air Forces Material Division, Oliver P. Echols, for being inadequate to military service; it was not judged powerful enough for the increased weight it would have after being constructed out of metal per AAF requirements. Roosevelt and the group of aviators, however, expressed appreciation for the D-2. When Roosevelt returned to the East Coast, Meyer hosted another round of parties and nightclub outings in Manhattan, and arranged for Fay Emerson to accompany Roosevelt. Meyer gave Emerson $132 worth of nylon stockings, a rare treat during wartime rationing.
On August 20, Roosevelt sent a report to General Arnold recommending immediate purchase of the D-2. On September 1, Arnold ordered Echols to contract with Hughes for an all-metal reconnaissance aircraft "against my better judgment and the advice of my staff." Major General Charles E. Bradshaw wrote to Arnold to suggest that the Lockheed XP-58 Chain Lightning was much farther along in development and could outperform the D-2 in every important aspect, but was unsuccessful in halting the Hughes contract. Implicating Roosevelt and United States Secretary of Commerce Jesse H. Jones, Assistant Secretary of War Robert A. Lovett noted to Major General Bennett E. Meyers that "Hughes has got powerful friends here in Washington" and that, if the background of the contract were uncovered, "there's going to be an awful smell." Nonetheless, Hughes was given $43 million (worth $}} million today) to build 100 all-metal aircraft, to be designated the Hughes XF-11.
In 1947, Roosevelt telephoned Hughes to warn him that a Senate subcommittee intended to call them both to account for financial irregularities regarding the XF-11 as well as for Hughes's H-4 Hercules, also known as the "Spruce Goose". As part of the ongoing "Investigation of the National Defense Program", on August 4, 1947 the subcommittee called Roosevelt and Meyer to testify about the Hollywood and Manhattan parties and women that Meyer had arranged and paid for. Meyer's financial records during such parties showed him paying $200 for "presents for four girls" and $50 for "girls at hotel (late)." At one point, Roosevelt asked Meyer whether "any of those girls who were paid, were they procured for my entertainment?" Meyer responded "I don't like the word 'procured,' because a girl who attends a party and is given a present is not necessarily 'procured.' " The committee found that Meyer had spent at least $1,000 in picking up Roosevelt's hotel bills as well as his nightclub and party checks, and Faye Emerson's bets at Agua Caliente Racetrack, and that Meyer had arranged for weekends in Palm Springs and Washington, D.C. for Roosevelt and Emerson, who eventually married in December 1944 after Roosevelt divorced his second wife in March 1944. All told, Meyer reported to the committee that he had spent $5,083.79 ($}} in today's dollars) on entertainment for Roosevelt. In his own defense, Roosevelt testified that he had never heard of the XF-11 until "Hap" Arnold let him know about it, and that several of the parties appeared to have taken place on days when he was out of the country on active duty. Roosevelt said "If it is true that for the price of entertainment I made recommendations which would have in any way endangered the lives of the men under me . . . that fact should be made known to the public."