Naval day fighters from El Segundo, part 2: the Douglas F6D Missileer

As I have discussed previously, the El Segundo division of Douglas made its only genuine forays into developing and building carrier-based jet fighters for operations in the daytime in the 1950s with the F4D Skyray and F5D Skylancer, both of which were quite revolutionary among US Navy jet fighters in their wing planform. However, the end of the F5D program and the completion of production of the F4D did not entirely spell the end of the flirtation by Douglas' El Segundo division with air-to-air combat aircraft designs, despite the company’s preoccupation with production of airliners, attack aircraft, and military transports. Towards the end of the 1950s, Douglas toyed with the idea of a long-range  interceptor designed to defend the US Navy’s aircraft carriers from Mach 2 capable aircraft, taking the world of long-range aerial interception into the realm of naval aviation. However, the concept of a subsonic fleet defense fighter by Douglas would end up being killed by a combination of both politics and the changing threat environment emanating from the Soviet Union.

An artist's concept of the Douglas F6D Missileer (D-766) in flight

In 1957, the US Navy published detailed assessments indicating that the new F4H Phantom II supersonic jet fighter might not be capable of protecting aircraft carriers from enemy aircraft capable of Mach 2 and that a purpose-built subsonic interceptor would be needed to prevent attacks on large carriers by Mach 2 aircraft. To begin addressing this demand, a new long-range air-to-air missile, the XAAM-N-10 Eagle, was envisaged with mid-course and terminal homing guidance systems and the capability to shoot down enemy aircraft 130 miles (209 km) away, and Bendix and Douglas submitted proposals for the airframe of the Eagle missile, the latter submission designated D-742 by Douglas. In December 1958, Bendix was selected by the Navy to build the Eagle, which relied on a solid-fuel rocket booster with folding fins to reach Mach 3.5, and Grumman became the sub-contractor for development of the XAAM-N-10. By late November 1959, the US Navy announced the TS-151 requirement for a long-range fleet defense jet fighter armed with the Eagle missile and equipped with a Westinghouse AN/APG-81 pulse-doppler radar while flying at a loiter time of six hours over a distance of 150 miles (241 km). In response, Boeing, Douglas, Grumman, North American, McDonnell, and Vought submitted bids for the TS-151 competition, with the Douglas proposals being designated D-765, D-766, and D-767 by the company and the North American design featuring straight shoulder-mounted wings and two jet engines slung under the wings. Douglas had previously worked on a subsonic long-range interceptor project in May 1958 under the internal designation D-746, the weapon system based on the carriage of the losing Douglas bid for the XAAM-N-10 airframe contract having been designated D-745. The D-766 design had straight shoulder-mounted wings and horizontal stabilizers and two Pratt & Whitney TF30 turbofans in the wing roots, and it was 53 feet (16.15 meters) long with a wingspan of 70 feet (21.3 meters), a height of 10 feet 1 in (3.07 meters), a wing area of 630 square feet (59 m²), a gross weight of 50,000 lb (22,680 kg), a maximum takeoff weight of 60,000 lb (27,216 kg), and a top speed of 546 mph (879 km/h). The wings of the D-766 would have underwing pylons for six Eagle air-to-air missiles, three per wing, and the tricycle landing gear had twin wheels on each leg, all folding into the fuselage.

  

A model of the Douglas F6D Missileer photographed by me at the Lyon Air Museum in late November 2021 

On July 21, 1960, the US Navy declared the Douglas D-766 the winner of the TS-151 competition, with the Vought V-434 submission achieving second place, and the D-766 was officially designated XF6D-1 and christened Missileer, with two prototypes ordered. The biggest complexity of the F6D Missileer was the fact that its pulse-doppler radar and air-to-air weaponry had to work in concert with the newly deployed Grumman W2F Hawkeye airborne early warning aircraft (redesignated E-2 in 1962), given that the AEW system of the Hawkeye was capable of detecting threats at ranges beyond 230 miles (370 km) to assist the F6D in intercepting enemy aircraft and the pulse-doppler radar could cover areas over distances of 137 miles (220 km). Therefore, although development of the F6D was seen as likely to be low-cost and successful, the system as a whole was very risky and expensive. Additionally, some Navy officials had doubts about the need for a subsonic fleet defense interceptor, arguing that once the F6D Missileer fired its missiles, it would be completely unable to defend itself and would have to return to an aircraft carrier as quickly as possible to re-arm. By December 1960 outgoing Secretary of Defense Thomas Gates removed funding for the F6D from the FY 1962 defense budget, and even though Douglas in February 1961 made a last-minute plea to keep the Missileer project alive, newly sworn-in Defense Secretary Robert McNamara formally canceled the F6D program in favor having the Navy and US Air Force forge a joint requirement for a new fighter-bomber that became the TFX program, which led to the F-111 Aardvark. The Eagle AAM that would have armed the F6D also was cancelled without ever having reached the hardware phase, but some of its technologies would later find their way into the AIM-54 Phoenix air-to-air missile carried by the F-14 Tomcat. In any case, the fact that the USSR did not put much serious effort into developing supersonic aircraft that could attack the carriers from which the F6D would have operated further poured cold water on the idea of a long-range fleet defense interceptor.

References:

Buttler, T., 2007. American Secret Projects: Fighters and Interceptors 1945 to 1978. Hinckley, UK: Midland Publishing.

Thomason, T.H., 2008. U.S. Naval Air Superiority: Development of Shipborne Jet Fighters, 1943–1962. North Branch, MN: Specialty Press.

Wagner, R., 2004. American Combat Planes of the 20th Century: A Comprehensive Reference. Reno, Nevada: Jack Bacon & Co. ISBN 0-930083-17-2.

Naval day fighters from El Segundo, part 1: Douglas F4D Skyray and F5D Skylancer

The United States Navy in the 1950s deployed a array of outstanding jet fighters for air-t-air combat in the daylight, including the Grumman F9F Cougar/Panther series, Vought F7U Cutlass and F8U Crusader, and McDonnell F3H Demon, not to mention that it acquired a navalized version of the North American F-86 Sabre as the FJ-2/3/4 Fury (which almost shared nothing in common with the earlier straight-wing FJ-1 Fury). However, somewhat lost in talk of US naval fighter aviation in the 1950s is the fact that a few naval jet fighter designs were conceived in the Los Angeles basin in southern California during the early Cold War, the Douglas F4D (F-6) Skyray and F5D Skylancer interceptors as well as the Douglas F6D Missileer fleet defense fighter project. This post will be the first of a two-post series concerning the 1950s jet fighter designs of the El Segundo Division of Douglas, mostly centering upon the development and operational service of the F4D and F5D.  

Models of the Douglas F4D Skyray and its supersonic derivative, the F5D Skylancer, photographed by me at the Lyon Air Museum in December 2021

In late December 1946, the chief designer at Douglas Aircraft's El Segundo, Ed Heinemann (famous for designing the SBD Dauntless, A-1 Skyraider, A-3 Skywarrior, and A-4 Skyhawk), proposed a tailless delta-wing jet interceptor under the company design D-571, capitalizing on captured wartime German aeronautical research regarding the benefits of delta wings. The initial D-571 design was a tailless flying wing with a single vertical stabilizer, two Westinghouse 24C turbojets, and four 20 mm cannons in the nose. Although the US Navy's Bureau of Aeronautics (BuAer) was delighted with the layout of the airframe, it was concerned about developmental problems with the Westinghouse engines and suggested that Douglas consider fitting the D-571 with the Rolls-Royce Nene instead. On February 14, 1947, the Navy gave Douglas an engineering contract for development for the D-571, including constructing a full-scale mock-up, and two new D-571 designs were worked out, the D-571-1 with two Westinghouse 24Cs and the D-571-2 with one Rolls-Royce Nene. Both proposals differed from the initial D-571 design in having the cockpit moved forward to give better visibility, greater space in the nose for alternative armament including spin-stabilized rockets, and utilizing the afterburner for climb to altitude rather than supersonic speeds. Although specifications for the D-571-1 and D-571-2 are given in Buttler (2013) and need not be discussed in depth, the two proposals had the same length but differed in wingspan, wing area, and gross weight.

The first Douglas XF4D-1 prototype (BuNo 124586) on the deck of the USS Coral Sea carrier in October 1953

On June 17, 1947, Douglas was awarded a preliminary contract to construct two D-571-1 prototypes (BuNos 124586/124587) under the designation XF4D-1. In March 1948, Douglas made adjustments to the XF4D-1 design to create the D-571-4, including rounded delta wing edges and the replacement of the Westinghouse engines with a single Westinghouse J40 turbojet, and these changes were tailored to allow the XF4D-1 design to meet the parameters of the OS-113 specification issued by the Navy in May for a high-performance interceptor to climb rapidly to altitude to intercept enemy bombers, thus leading to the XF4D-1 prototype contract being emended on December 16, 1948 to cover the D-571-4 rather than the D-571-1. The XF4D-1 was officially christened Skyray by the Navy, and although the first XF4D-1 prototype was completed in 1950, the J40 was not yet available and Douglas decided to power the two prototypes with one Allison J35 turbojet, clearing the way for the first flight of the Skyray on January 23, 1951. The next month, the Navy ordered an initial production batch of twelve F4D-1s (BuNos 130740/130751), and when the Westinghouse J40 finally became available in 1952, the two Skyray prototypes were re-engined with the J40. On October 3, 1953, the second XF4D-1 became the first carrier-based aircraft in history to break the sound barrier when it attained a speed of 753 mph (1,212 km/h) while flying over the Salton Sea in California. The F4D Skyray was 45 feet 4 in (13.82 meters) long, with a wingspan of 33 feet 5 in (10.18 meters), a height of 13 feet (3.96 meters), a wing area of 557 square feet (51.8 m²), a top speed of 722 mph (1,162 km/h), and armament comprising four 20 mm cannons or 76 unguided air-to-air rockets. In the spring of 1952, the Navy placed an additional production order for F4D Skyray when it ordered 230 F4D-1s (BuNos 134744/134973). 

Left: A Douglas F4D-1 Skyray (BuNo 139097) over San Diego Bay, 1960
Right: An F4D-1 Skyray landing aboard the aircraft carrier USS Bon Homme Richard on August 30, 1957

Even before the XF4D-1 broke the sound barrier, however, it was clear to Douglas and the Navy that the J40 turbojet was becoming prone to inflight fires and explosions as well as its inability to produce the expected thrust output. Therefore, in March 1953, the US Navy decided to have production F4Ds fitted with the Pratt & Whitney J57 turbojet, which was more reliable and powerful than the J40, but the J57 was so large and heavy that 80 percent of the F4D airframe had to be redesigned to accommodate this powerplant. As developmental of the production F4D-1 got underway, the XF4D-1 was used for carrier qualification trials aboard the USS Coral Sea, with tests performed by Lieutenant Commander James Verdin in fairly poor weather, and these conditions made it possible to test the aircraft's low-speed stability on approach with its leading-edge slats. On June 5, 1954, the first production F4D took to the skies, going supersonic in a brief dive, but flight testing revealed frequent engine stalls at high speeds above 40,000 feet (12,192 meters), prompting modification  of the geometry of the air intakes and addition of an airflow baffle plate ahead of each air intake to alleviate this problem. Changes were also made to the fairing around the afterburner exhaust to make the airflow smoother, eliminating a high-speed turbulence problem that had been encountered during early flight tests of the F4D-1. The F4D began reaching US Navy squadrons in April 1956, and it entered service with the US Marine Corps in early 1957; Navy pilots nicknamed the Skyray the "Ford" in reference to its designation. An additional 408 F4D-1s were ordered (BuNos 136163/136392 and 139030/139207), but only BuNos 139030/139207 were completed, while BuNos 136163/136392 were canceled, and deliveries of the F4D Skyray continued until December 22, 1958, by which a total of 422 examples had been completed (two prototypes and 420 production aircraft).  Late production F4Ds were fitted with the more powerful J57-P-8 and had seven hardpoints for external weapons loads, three under each wing and one on the ventral fuselage centerline. Underwing loads could consist of six pods, each containing seven 2.75-inch unguided rockets, four pods each containing nineteen 2.75-inch rockets each, two 2,000 lb (907 kg) bombs, or two Sidewinder air-to-air missiles. A proposal to fit the F4D-1 with one J57-P-14, designated F4D-2, did not progress beyond the design phase. On May 22 on 23, 1958, US Marine Corps Major Edward N. LeFaivre set five time-to-height records in F4D-1 BuNo 130745:  9,842.5 feet (3,000 meters) in 44.39 seconds, 19,685 feet (6,000 meters) in 1 minute 6.13 seconds, 29,527.5 feet (9,000 meters) in 1 minute 29.81 seconds, 39,370 feet (12,000 meters) in 1 minute 51.23 seconds, and 49,212.5 feet (15,000 meters) in 2 minutes 36.05 seconds. 

A Douglas F4D/F-6A Skyray of the US Marine Corps operating from Leeward Point Field, Guantanamo Bay, Cuba, in early 1963

Despite having a good climb rate, high service ceiling, high speed, and powerful interception radar, the F4D Skyray had a brief operational career because it was only designed for high-altitude interception and lacked the multi-mission capabilities of newly developed US Navy fighters like the F8U Crusader and F4H Phantom II. Indeed, a 1957 Navy evaluation report found the F4D-1 only marginally effective as an all-weather fighter, identifying deficiencies like a modest top speed capability, poor transonic flying qualities, and armament control system limitations. Moreover, the Skyray had not been built for supersonic flight and could only exceed Mach 1 in brief dives. The F4D was deployed to Taiwan in late 1958 in response to China's air war over the Taiwan Straits, and to the Guantanamo Bay Naval Base in southeastern Cuba in October 1962 in response to the USSR's deployment of medium-range ballistic missiles in Cuba the same month, but never saw any combat. One F4D-1 (BuNo 134759) was loaned to the NACA Ames Aeronautical Laboratory (now NASA Ames Research Center) at NAS Moffett Field, California, for aerodynamic research beginning on April 4, 1956, and it was used for flying qualities, stability and control, and performance evaluations until October 16, 1959. When the Department of Defense introduced the Tri-Service designation system in September 1962, the F4D was redesignated F-6A. After eight years of operational service, the Skyray was retired from operational Navy service on February 29, 1964.

The first Douglas XF5D-1 Skylancer prototype (BuNo 139208) during its first flight on April 21, 1956 

While the Skyray was just beginning to enter production, Douglas proposed an all-weather variant of the F4D-1 for supersonic flight, also designated F4D-2. This design retained the delta wing shape and fuselage of the production Skyray but differed in having thinner wings with reinforced skins to reduce transonic drag following the Whitcomb area rule, redesigned air intakes, and a taller vertical stabilizer, and it had an empty weight of 17,444 lb (7,912 kg), a gross weight of 28,739 lb (13,036 kg), and a top speed of 789 mph (1,270 km/h) at an altitude of 35,000 feet (11,000 meters). Armament consisted of four 20 mm cannons in the wing roots, 72 spin-stabilized unguided 2 inch (51 mm) rockets, and either four AAM-N-7 Sidewinder or two AAM-N-3 Sparrow II air-to-air missiles. The Navy decided that the F4D-2 was sufficiently distinct from the F4D to be given a new designation, XF5D-1, and two XF5D-1 prototypes (BuNos 139208/139209) were ordered in October 1953. Nine YF5D-1 service test aircraft (BuNos 142349/142357) and 51 production F5D-1s (BuNos 143393/143400 and 145159/145201) were ordered in 1955, and the prototypes and service test aircraft were powered by one Pratt & Whitney J57-P-8, while the production version was to be powered by one J57-P-14. The first Skylancer prototype made its first flight on April 21, 1956, piloted by Robert Rhan, and it was engineered well enough to break the sound barrier on its maiden flight. Compared to the F4D Skyray, the F5D was capable of flying supersonically at maximum altitude and had twice the operating range of the Skyray, and Douglas also proposed to fit later production F5Ds with the General Electric J79 turbojet, but that scheme did not win orders from the Navy. Despite the stellar performance of the Skylancer, the Navy terminated the F5D program in 1957 because the supersonic day fighter role for which the Skylancer was fulfilled by the Vought F8U Crusader, which had just entered deployment in March 1957, and by then the first two service test F5Ds had been completed, leaving the Navy to cancel the remaining YF5D-1s on order as well as contracts for the production aircraft. Moreover, the US Navy saw to it that Douglas was preoccupied with production of the AD Skyraider, A3D Skywarrior, A4D Skyhawk, and F4D Skyray, finding it to be against its conscience to give Douglas a monopoly on Navy combat plane production. 

Left: The second YF5D-1 (BuNo 142350) in flight with tail code NASA 802
Right: The first F5D Skylancer prototype on the tarmac at an airfield in Ontario, Oregon, with tail code NASA 708, seen here in April 2004 

After the Skylancer program was shelved, the F5Ds were given to NACA at Moffett Federal Airfield in Mountain View, northern California, on August 20, 1957, for flight research-related activities. The first XF5D and second YF5D-1 received the tail codes NACA 212 (later changed to NASA 212 in 1958, then NASA 708) and NACA 213 (later changed to NASA 213 in 1958, then NASA 802) respectively, operating at Moffett Federal Airfield until 1961 when they were assigned to Edwards AFB for tests of new radar systems, instruments and armament. While the second XF5D and first YF5D were grounded in 1961 to provide spare parts, the other two F5Ds were transferred to the NASA Ames Research Center in 1963 for testing the ogival delta wing for some American supersonic airliner designs and training pilots for the canceled Boeing X-20 Dyna-Soar military spaceplane program. The first F5D prototype was retired in April 1968, and the the second YF5D was used as a chase plane for lifting body aircraft and in support of SST design studies following the cancellation of the X-20 program, flying until 1970, when it was retired in 1970. The first F5D prototype subsequently became part of Merle Maine's private collection in Ontario, Oregon, until 2014, when it was transferred to the Evergreen Aviation Museum in McMinnville, Oregon, while the second YF5D is now on static display outside of the Armstrong Air & Space Museum in Wapakoneta, Ohio (the hometown of Neil Armstrong, the first man to set foot on the Moon).

A three view drawing of the Douglas D-652-1 variant of the D-652 submission to the OS-130 competition won by the Vought F8U Crusader

As a side note, in early 1953 Douglas proposed a supersonic jet fighter derived from the F4D Skyray for the Navy's OS-130 requirement under the company designation D-652. Four D-652 designs were worked out, the D-652 sans suffixe with a longer fuselage and thin wings to reduce transonic drag as well as a Pratt & Whitney J57 turbojet, the slightly scaled down D-652A with a shorter nose and one Rolls-Royce Avon turbojet, the D-652-1 with the cockpit moved forward to allow more space for fuel in the fuselage, and the D-652-2 with the same airframe as the F4D but largely differing in electronics and external fuel tanks. Both the D-652-1, and D-652-2 proposals would have used either the J57 or Avon, and these designs along with the D-652A differed from the baseline D-652 in having a shorter nose. However, in May 1953, the competing Vought V-383 proposal was declared the winner of the OS-130 competition and became the F8U Crusader, making its first flight in May 1955.

References:

Buttler, T., 2013. Early US Jet Fighters: Proposals, Projects, and Prototypes. Manchester, UK: Hikoki Publications. 

Frankel, M., 2010. Killer Rays: Story of the Douglas F4D Skyray & F5D Skylancer. North Branch, MN: Specialty Press.

Competitors to the B-29 from southern California: Lockheed XB-30, Douglas XB-31, and Consolidated B-32 Dominator

The Boeing B-29 Superfortress long-range strategic bomber is best known in the annals of military history as the US heavy bomber that carried out carpet-bombing raids on Japan in the final months of the Pacific theater of World War II and brought about the ultimate finale to human history's most destructive conflict by dropping atomic bombs on Hiroshima and Nagasaki, which forced Japan to surrender for the first time in its military history on August 14, 1945. However, the B-29 was not a standalone development when it came to fulfilling military aviation requirements for a long-range heavy bomber with greater range and bombload than the B-17 or B-24. In southern California, three aircraft manufacturers --- Consolidated, Douglas, and Lockheed --- came out with heavy bomber designs to compete with the B-29, but only one was selected for full-scale development and became the Consolidated B-32 Dominator. Since the B-32 entered production but only got as far as limited full-scale production before war's end, I am opting to give a comprehensive synopsis of the rival designs to the B-29 envisaged in southern California, including the B-32.

The Boeing B-29 Superfortress, which along with the Consolidated B-32 Dominator won the R-40B competition of 1940.

On November 10, 1939, two months after Germany invaded Poland, US Army Air Corps General Henry "Hap" Arnold requested authorization to contract with major aircraft companies for studies of a Very Long-Range (VLR) bomber to strike enemy targets over greater distances than the B-17 Flying Fortress and B-24 Liberator. In December, the USAAC issued the VLR "superbomber" requirement for a new strategic bomber with a top speed of 400 mph (640 km/h) and able to carry 20,000 lb (9,100 kg) of bombs over a range of 2,667 miles (4,292 km). On January 29, 1940, the War Department issued Request for Data R-40B based on this requirement and circulated it to Boeing, Consolidated, Douglas, and Lockheed, and on April 8, Specification XC-218A was issued which also required additional defensive armament, armor, and self-sealing tanks. 

Left: A wind tunnel model of the Lockheed XB-30 heavy bomber derivative of the Constellation airliner.
Right: Side view of the Douglas XB-31 project, designated Model 332F by Douglas (courtesy of Alan Griffith).

Three companies based in southern California submitted bids for the R-40B competition. Consolidated's design, the Model 33, was a scaled-up B-24 Liberator derived from the company's initial LB-25 design study of late 1939/early 1940, while Lockheed submitted the L-117 (Model 51-58) derivative of the Constellation airliner with a length of 104 feet 8 in (31.91 meters), a wingspan of 123 feet (37.50 meters), a wing area of 1,646 square feet (153 m²), empty and gross weights of 51,616 lb (23,462 kg) and 85,844 lb (39,020 kg) respectively, and armament comprising ten .50 in (12.7 mm) machine guns (eight in four fuselage turrets and two in a single nose turret) and one 20 mm cannon in a remote-controlled tail turret. Douglas envisaged a series of design studies under the internal designation Model 332, all of them resembling a scaled-up A-20 Havoc and distinguished by their tail empennage layouts and engines; the Model 332F submitted for the R-40B was 88 feet 8.5 in (27.04 meters) long with a wingspan of 140 feet 6 in (42.82 meters), a wing area of 1,780 square feet (165.54 square meters), gross and maximum take-off weights of 106,994 lb (48,532 kg) and 120,000 lb (54,432 kg) respectively, and armament comprising seven pairs of 0.50-in (12.70 mm) machine guns (four in pairs facing rearwards in the rear of the outboard engine nacelles, and three in dorsal and ventral turrets below the fuselage) and one 20 mm cannon in the tail. On June 27, 1940, the Lockheed L-117, Douglas Model 332F, and Consolidated Model 33 submissions were designated XB-30, XB-31, and XB-32 respectively, and like the Boeing Model 345 (which became the XB-29), they were powered by four Wright R-3350 Duplex Cyclone radial piston engines. Some older sources (e.g. Francillon 1979; Jones 1984) identify the Douglas Model 423 intercontinental bomber project of October 1941 as the XB-31, but as noted by Buttler and Griffith (2015), the Model 423 was conceived in response to the 1941 intercontinental bomber competition won by the Northrop XB-35 and Convair B-36 Peacemaker and thus never received a military designation.

Top left: The first XB-32 prototype (serial number 41-141) taxiing at Lindbergh Field, San Diego, early September 1942
Top right: The second XB-32 prototype (serial number 41-142) in flight, July 1943
Bottom: The third XB-32 prototype (41-18336) (note the newly installed tall vertical stabilizer that offered better directional stability compared to the initial twin-fin tail empennage and B-29 type vertical stabilizer) during a test flight with the propellers of the port engines feathered in mid-1944.. 

In July 1940, the USAAC announced that the XB-29 and XB-32 had won the R-40B competition, the XB-30 and XB-31 submission having been withdrawn due to Lockheed and Douglas being preoccupied with production of the A-20, P-38, Hudson, and DC-3. On September 6, 1940, a contract was signed for two XB-32 prototypes (serial numbers 41-141/142) at the same time that two XB-29 prototypes were ordered, and a third prototype (serial number 41-18336) was added in November. Mock-ups of the XB-32 was built in late December and later inspected and approved January 6, 1941, after a few structural changes, and thirteen YB-32s (serial numbers 42-108471/108484) were ordered on June 30. The XB-32 was 82 feet 1 in (25.02 meters) long with a wingspan of 135 feet (41.15 meters), a height of 20 feet 10 in (6.35 meters), a wing area of 1,422 square feet (132.1 m²), a gross weight of 101,662 lb (46,113 kg), a top speed of 376 mph (605 km/h), and twelve crewmen, with armament comprising fourteen 0.50 in (12.70 mm) machine guns and two 20 mm cannons (eight in the upper and lower gun turrets, two in the wing's leading edges outboard of the propellers, and four 0.50 in [12.70 mm] machine guns and two 20 mm cannons at the rear of the outboard engine nacelles in rearward firing positions and controlled by aiming stations in the fuselage and tail). It was similar to the B-24 Liberator in its tail empennage, high-mounted Davis-type wing, and twin bomb bays covered over by roll-up doors, but differed in having a cylindrical fuselage, larger wing, and a stepped cockpit nose section. The first XB-32 prototype was rolled out on September 1, 1942, making its first flight from Lindbergh Field, San Diego, on September 7, two weeks before the B-29. However, a number of developmental problems with the fire control system and in February 1943 the YB-32 contract was canceled, but a month later, an order was placed for 300 production B-32s (serial numbers 42-108471/108770) to be built at the Consolidated plant in Forth Worth, Texas.* The first XB-32 crashed shortly after takeoff on May 10 due to a flap malfunction, killing the test pilot and injuring six crewmen, dealing a setback to the B-32 flight test program. The second XB-32 prototype, which first flew on July 2, had modified rudder tabs, a pressurized cabin,  remote-controlled retractable gun turrets in the dorsal and ventral positions, and a manned tail turret, and it was transferred to Muroc Army Air Field (now Edwards Air Force Base) in February 1944 for acceptance tests after thirty test flights. The third XB-32 prototype first flew on September 17, 1943 and differed from the first two prototypes in having ten machine guns in the nose, dorsal, ventral, and tail turrets. Due to longitudinal stability problems after 25 test flights, this aircraft was fitted with the single vertical stabilizer designed for the B-29 in November 1943 and first flown with this new tail empennage on January 6, 1944, but this vertical tail was deemed to offer marginal stability, so an even taller vertical stabilizer measuring 19 feet 4.28 in (5.9 meters) high was installed on the third XB-32, which first flew with this vertical tall in the spring of 1944. The B-32 was initially named Terminator in late 1943 at the behest of Consolidated, but the US Army Air Force's Aircraft Naming Board changed the name to Dominator; the State Department eventually had the B-32 revert to its initial name for the sake of "political correctness", but the name Dominator tends to persist in most aviation literature for the B-32.

* After the cancellation of the YB-32 contract, the serial numbers allocated to the YB-32s were re-used for the first 13 production B-32s.

The first production B-32 Dominator (serial number 42-108471) in flight over Fort Worth, Texas, August 1944 

In June, the US Army Air Force increased the number of B-32s on order to 1,213 aircraft, including a batch of 500 B-32-1-CO aircraft (serial numbers 44-90486/90985) to be built at the Convair factory in San Diego, and it changed the B-32's official name to Dominator. The first two production B-32s, of which the first flew on August 5, 1944, were initially fitted with the vertical stabilizer from the B-29, but the latest single vertical stabilizer built for the third XB-32 was eventually fitted to these aircraft. The production B-32 had a ten-man crew, a maximum bombload of 20,000 lb (9,071 kg), a maximum range of 4,421 miles (7,114 km), and defensive armament comprising ten 0.50 in (12.70 mm) Browning M2 machine guns in five power-operated turrets (four in two Martin turrets on the top of the fuselage, four in Sperry ball turrets on the nose and in the tail, and two in a retractable belly turret). Deliveries of the B-32 to US Army Air Force began in September 1944, but by then the B-29 had begun combat missions over Japan, and although the B-32 had been touted by the USAAF as a back-up in the event that the favored B-29 failed, the success made by Boeing in helping the B-29 overcome engine troubles during flight testing as well as delays and deficiencies in the B-32 program prompted several USAAF officials to recommend that the B-32 program be cancelled outright. By the end of 1944, only fourteen B-32s were delivered to the USAAF, and they even experienced mechanical malfunctions, while complaints were made about faulty workmanship on some of the delivered aircraft. However, in December, Brigadier General Donald Wilson recommended that despite these difficulties it would be unwise to abandon the B-Dominator program until a full set of tests had conclusively demonstrated its unsuitability, and no final decision about the Dominator's future be made until after the completion of service tests, allowing for the crew training program should continue. From January to March 1945, forty B-32s (serial numbers 42-108485/108524) were delivered to the USAAF without gun turrets or bombing equipment for B-32 crew training  and officially designated TB-32. Prospective B-32 pilots underwent 50 hours training in TB-32s and co-pilots received 25 hours of flight time and 25 hours of observer training. The first B-32 to be built in San Diego was flown on March 17, 1945, but following Nazi Germany's surrender on May 8, orders for the B-32 were reduced to 214 aircraft from Fort Worth. Lieutenant General George C. Kenney of the Fifth Air Force had been anxious to acquire B-29s, but when his requests were turned down on the grounds that the B-29 was urgently needed elsewhere, he started requesting B-32s instead. On March 27, 1945, General Henry "Hap" Arnold approved Kenney's request and authorized the USAAF to carry out comprehensive combat tests of the B-32 Dominator. Three B-32s were dispatched to the 386th Bombardment Squadron of the 312th Bombardment Group based on Luzon, Philippines, on May 24-25, 1945, to begin combat testing, and on May 29 the B-32 carried out its first combat mission when two of the three B-32s (42-108529 and 42-108532) attacked a Japanese supply depot in Luzon's Cayagan Valley, followed by a series of strikes in June on targets in Formosa (now Taiwan) and Hainan Island (B-32 serial number 42-108528 did not take part in the May 29 mission because it made an abort during take-off). The B-32s encountered no real enemy opposition except for inaccurate enemy flak, and they returned to their base safely. 

Convair B-32 Dominator Hobo Queen II (serial number 41-108578), which carried out the last combat mission by an Allied aircraft in World War II.

Following the success of the first B-32 combat mission, the 386th Bombardment Squadron made plans to transition from the A-20 Havoc to the B-32, and the 387th Bombardment Squadron began following suit, with eventual plans to relocate the 312th Bombardment Group to Okinawa. Before the conversion could be carried out, however, the dropping of the atomic bombs on Hiroshima and Nagasaki in early August 1945 led to the 312th BG being moved to Okinawa immediately, and six more B-32s joined the squadron on Okinawa a few days later. Combat operations continued in spite of the de-facto cease-fire that had been called following the bombing of Nagasaki, and August 17, four B-32s carrying out a photographic reconnaissance mission over Tokyo to confirm Japan's surrender were fired upon on by radar-directed flak and attacked by Japanese fighters, but suffered only minor damage, claiming three air-to-air kills (two A6M Zeroes and one N1K-J Shiden-Kai). On August 18, the B-32 Hobo Queen II (serial number 42-108532) and a second B-32 (serial number 42-108578) were attacked by Japanese fighters, and tail gunners claimed three air-to-air kills (two A6M Zeroes and one N1K-J Siden-Kai), but Japanese fighters heavily damaged 42-108578, killing Sergeant Anthony Marcione and wounding two more men, including photographer Staff Sergeant Joseph Lacharite. Nonetheless, 42-108578 returned to its base in Okinawa, and the Japanese fighters downed by the B-32s on August 18 constituted the last Axis warplanes to be shot down by American (and more broadly Allied) combat aircraft in World War II.  The last B-32 photographic reconnaissance mission was conducted on August 28, during which two B-32s were destroyed in separate accidents, with 15 of the 26 crewmen killed. Two days later, the 386th Bombardment Squadron stood down from operations, and with the end of the Pacific theater of World War II, unfulfilled B-32 orders were cancelled on September 8 and production of the B-32 halted on October 12. By this time, 115 production B-32s had been delivered (114 from Fort Worth and one from San Diego), while twelve additional aircraft (42-108585/108594, 44-90487/90488) were completed but not delivered, and no fewer than 49 B-32s were nearing completion at Fort Worth. All the B-32s that were operational as well as the undelivered aircraft were flown to storage at a disposal and reclamation center in Walnut Ridge, Arkansas, in 1946, and most of them were scrapped by 1947. One B-32 (serial number 42-108474) was set aside for future display at the National Museum of the US Air Force in Dayton, Ohio, but this plan never materialized and the aircraft was scrapped at Davis-Monthan Air Force Base in Tucson, Arizona, in August 1949. Nevertheless, a few B-32 components survive today, including a B-32 nose turret in storage at the Paul Garber Restoration Facility of the Smithsonian Institution at Suitland, Maryland, another B-32 nose turret on display at the Minnesota Air and Space Museum, and a static test wing panel from a B-32 erected as a monument to aviation pioneer John J. Montgomery on a hill near San Diego.

Two advanced B-32 (Model 33) studies that never were: a cutaway view of a four engine maritime reconnaissance project dated April 28, 1945 (left) and an artist's conception of early B-32 airliner proposal conceived in December 1941 (right)   

In an interesting footnote, several unbuilt variants of the B-32 Dominator were envisaged by Convair for maritime patrol and transport, along with a proposed turboprop-powered version. As early as mid-1941, a passenger airliner variant of the B-32 was conceived with a crew of six and accommodations for 78 passengers in daytime operations or 34 passengers at night, and in 1943, two military transport versions of the B-32 were devised, one which looked like a slightly smaller Convair XC-99 and which would have been used as either a troop transport, a hospital MEDEVAC aircraft, a paratrooper aircraft, or a cargo transport for carrying howitzers, aircraft, military jeeps, anti-tank guns, and/or ammo trucks. The latter design was also envisaged in September 1943 as a 58 passenger airliner, and design studies were also conducted for a B-32 escort aircraft (similar to the Boeing XB-40 and the Consolidated XB-41), a variant powered by four General Electric TG-100 (T31) turboprops, a twin-engine B-32 proposal, and a four-engine maritime reconnaissance B-32 variant armed with ten 0.50 in (12.70 mm) machine guns (four in the forward and aft top fuselage turrets, two in a retractable bottom fuselage turret, and four in the nose and tail turrets) and provisions for photoflash bombs, mines, or depth charges in the bomb bay. However, due to delays in development and production of the B-32, none of these proposals ever materialized.

Although the Consolidated B-32 Dominator is one of the lesser-known American bomber aircraft of World War II due to the fact that it was intended as a back-up in the event of the failure of the B-29, only to nearly arrive too late for the war due to the success of the B-29, it nonetheless holds the honor of undertaking the last combat mission by an Allied aircraft in World War II, considering that the rival B-29 was instrumental in forcing Japan to surrender after repeatedly refusing to do despite defeats at Iwo Jima and Okinawa.       

References:

Andrade, J. M., 1979. US Military and Aircraft Designations and Serials since 1909. Leicester, UK: Midland Counties Publications.

Bradley, R., 2010. Convair Advanced Designs: Secret Projects from San Diego 1923-1962. North Branch, MN: Specialty Press.

Buttler, T., and Griffith, A., 2015. American Secret Projects: Fighters, Bombers, and Attack Aircraft, 1937-1945. Manchester, UK: Crecy Publishing. ISBN 978-1906537487.

Francillon, R. J., 1979. McDonnell Douglas aircraft since 1920, Volume 1. London, UK: Putnam Publishing.

Jones, L.S., 1984. U.S. Bombers: 1928 to 1980s. Fallbrook, CA: Aero Publishers.

Wolf, W., 2006. Consolidated B-32 Dominator: The Ultimate Look: from Drawing Board to Scrapyard. Atglen, PA: Schiffer Publishing.