The interception of the Rex was a training exercise and military aviation achievement of the United States Army Air Corps prior to World War II.

The tracking and location of an ocean-going vessel (the Italian liner SS Rex) by B-17 Flying Fortresses on 12 May 1938 was a major event in the development of a doctrine that led to a United States Air Force independent of the Army.

[1] The mission was ostensibly a training exercise for coastal defense of the United States, but was conceived by planners to be a well-publicized demonstration of the capabilities of "heavy bombers (as) long range instruments of power".

[2] The flight was conducted during coastal defense maneuvers held by the Air Corps without the participation of the United States Navy, and apparently without understanding of their purpose by the Army Chief of Staff.

Incurring the enmity of the Navy, which considered the achievement nothing more than a publicity stunt, Mitchell continued to discredit the battleship as the main weapon for projection of power by sinking several more obsolete ships in the next two years.

[n 2] However, the Air Service was limited by Army policy to being an auxiliary of the ground forces and was unable to obtain a role that would use long distance bombers.

[10] On 7 January 1931, Army Chief of Staff General Douglas MacArthur and Navy CNO Admiral William V. Pratt, reached an agreement modifying the joint action statement by assigning the coastal defense role for land-based aircraft to the Air Corps.

Further, the failure was witnessed by several dozen reporters, movie newsreel crews, a broadcast team from NBC radio, and observers from both the Army and Navy, some aboard airplanes that did find the ship.

[15] Hanson W. Baldwin, military editor of The New York Times and a Naval Academy graduate, averred that it was "illustrative of the inefficiency of land-based pilots over water".

Another old ship, the Haines, sank in shallow water while being towed off Plum Tree Island in Chesapeake Bay and became a hazard to navigation.

[20] On 4 March 1937, the 2nd Bombardment Group, now commanded by Lieutenant Colonel Robert Olds, received the first of the newly developed B-17 Flying Fortress heavy bombers,[21] with 12 delivered during the spring and summer of 1937.

[25] Authorized by a directive of President Roosevelt issued 10 July 1937, the exercise used the target ship Utah to represent a hostile fleet of two battleships, an aircraft carrier, and nine destroyers.

[27] Brigadier General Delos Emmons, commander of the GHQ Air Force's 1st Wing, dispatched bombers at 09:00 on 13 August to search an area of 30,000 square miles (78,000 km2) entirely covered by low clouds.

Accompanied by Major General Frank Andrews (commanding the GHQ Air Force), he flew in the lead B-17 above the clouds, patrolling an area 200 nautical miles (370 km) offshore.

[35] In an attempt to overcome this compartmentalization, Andrews bypassed the chain of command on 8 January 1938,[36] in a memorandum of his own regarding a minor joint air exercise held in November 1937 off the Virginia Capes.

Andrews sent a memo directly to Roosevelt's military aide, Colonel Edwin M. Watson, that included confidential Navy memoranda confirming the accuracy of the Army's bombing.

[38][n 4] 468 officers, 2,380 enlisted men, and 131 aircraft were drawn from all three wings of the GHQ Air Force[39][40] and based at 18 airports in the northeast United States, "from Schenectady, New York, and Aberdeen, Maryland, westward to Harrisburg, Pennsylvania".

[3] The Army publicized the resulting scenario as depicting simultaneous attacks on America by hostile fleets on both coasts, with the Air Corps tasked to defend against one of them.

[n 6] Eaker, who had a degree in journalism and had just completed a course in news photography at the University of Oklahoma, used the maneuvers as a platform for publicizing both the capabilities and materiel deficiencies of the Air Corps.

When newspapers, including the Los Angeles Times, criticized the maneuvers for using a "mythical fleet" as a target,[44] Hull suggested that an ocean liner be substituted for naval vessels.

LeMay's original flight plan had incorporated an area search if necessary, but weather conditions and the ship's distance from Long Island precluded that possibility.

[45] At noon the B-17s encountered an area of "scattered rain squalls",[48] spreading into a line abreast formation with the aircraft 15 nautical miles (28 km) apart to increase their chances of spotting the Rex.

Cousland's Flying Fortress encountered severe hail, damaging all the forward surfaces of the plane, and ice caused a temporary shutdown of one engine.

[58] On 3 August, the Army went on to cancel orders for 67 more B-17s authorized under a "balanced" plan Woodring himself had put forth in March, instead allocating the funds to buy smaller combat aircraft,[59] and forbade any further spending for R&D of long-range bombers.

[58] It was not until January 1939, when U.S. President Franklin D. Roosevelt issued a public statement calling for an expansion of the Air Corps in anticipation of the coming of World War II and the needs of the United States in defending the Western Hemisphere, that Army policy was reversed.

[63] The day after the rendezvous with the Rex, Chief of Staff General Malin Craig telephoned Andrews and issued an order that restricted all Air Corps aircraft to operating within 100 nautical miles (190 km) of the coast.

[51] Greer, however, in his history of Air Corps doctrine, firmly attributes the restriction to the Navy, noting that in November 1938 it achieved a new modification of the joint action statement specifically granting it the authorization for long-range land-based flights that the Army was denied, and immediately prepared six major bases to conduct them.

[66] A fourth historian, in a biography of Arnold, stated that the restriction had actually been promulgated on 1 September 1936, at the insistence of the Navy, but was not enforced by Craig until after the Rex incident.

[15] The Navy specifically included the 100 nautical miles (190 km) limit in plans for joint maneuvers in 1939 that was deleted only after Andrews objected to Marshall, who had replaced Embick as deputy chief of staff.

[79] Caleb V. Haynes and his crew won the MacKay Trophy in 1939 flying an earthquake relief mission to Chile in the Boeing XB-15, and delivered the first B-24 Liberator to the UK, pioneering the northern Atlantic route in July 1941.