Competitors to the B-47 Stratojet from southern California: the B-45 Tornado and XB-46

Much has been written about the Boeing B-47 Stratojet, the world's first multi-engine swept-wing jet bomber to go into production and operational service, especially with regards to its development, flight testing, and operational career. However, it should be emphasized that the B-47 was not a product of its own creation despite being the first American swept-wing jet bomber but instead was part of a years-long effort by the United States to shop for a gas turbine-powered strategic bomber to replace its fleets of B-17, B-24, and B-29 bombers through solicitations from different aircraft manufacturers, including Boeing. As a matter of fact, the aviation industry in southern California that manufactured the B-24 Liberator, B-25 Mitchell, and B-32 Dominator during World War II put out two rival designs to the B-47 Stratojet using the old-fashioned straight wing planform, the North American B-45 Tornado and the Convair XB-46. In an unusual twist of fate, the B-45 went into production, but the XB-46 remained at the prototype stage only.

Models of the North American B-45 Tornado (left) and Convair XB-46 (right) at the Lyon Air Museum, Chino (photographed by me in November 2021)

In 1944 the US Army Air Force became aware of Nazi Germany's fielding of the world's first jet bomber, the Arado Ar 234, so in March the US War Department issued a requirement for a multi-engine strategic jet bomber with a top speed of 500 mph (804 km/h), a range of 2,500-3,000 miles (4,023-4,828 km), a service ceiling of 35,000-40,000 feet (10,668-12,192 meters), and a 16,500 lb (7,484 kg) bombload. Four companies -- Boeing, Convair, Martin, and North American -- submitted bids for the intermediate-range strategic bomber requirement, with North American's proposal bearing the company designation NA-130 and the Convair submission being designated the Model 109 (later changed to Model 1). Both the NA-130 and Model 109 were straight-winged designs powered by four Allison J35 turbojets housed in pairs in two underwing nacelles. The designation XB-45 was allocated to the NA-130, and a contract for three XB-45 prototypes (serial numbers 45-59479/59481) was signed on September 8, 1944. Five months later, on February 27, 1945, three Convair Model 109 prototypes (serial numbers 45-59582/59584) were ordered and the Model 109 was officially designated XB-46. (The other submissions, the Boeing Model 432 and Martin Model 223 [designated XB-47 and XB-48 respectively], were designed outside southern California and thus are outside the scope of this blog.) Although the end of World War II caused many wartime aircraft projects and production orders to be cancelled, the War Department did not cancel the XB-45, XB-46, XB-47, and XB-48 programs, given its recognition that jet aircraft were the wave of the future.

Left: First North American XB-45 prototype (serial number 45-59479) in flight
Right: The sole Convair XB-46 prototype (serial number 45-59582) in flight

The XB-45 Tornado was 74 feet (22.55 meters) long with a wingspan of 89 feet 6 in (27.28 meters), a height of 25 feet 2 in (7.67 meters), a wing area of 1,175 square feet (109.2 square meters), an empty weight of 41,876 lb (18,953 kg), a gross weight of 66,820 lb (30,309 kg), and a maximum speed of 516 miles per hour (830 km/h). The engine nacelle arrangement adopted for the B-45 was reminiscent of that of the Arado Ar 234C four-engine variant of the Ar 234 jet bomber, and the nose of the XB-45 had window panels at the upper surface. The XB-45 crew comprised a pilot, co-pilot, bombardier/navigator, and a tail gunner; the pilot and co-pilot sat in a bubble cockpit canopy, while the bombardier/navigator sat in the nose and the tail gunner operated a tail gun turret. The XB-45 prototype made its first flight on March 17, 1947 (which happened to be St. Patrick's Day), and the three XB-45 prototypes (each instrumented for different specialized phases of the flight test program) carried out more than 130 test flights; the first XB-45 prototype crashed on take-off from Wright-Patterson Air Force Base in Dayton, Ohio, on June 28, 1949, due to a failure of the landing gear. The XB-46, on the other hand, had a very slender fuselage oval in cross-section and very high-aspect ratio wings, with its four J35s paired in two integral nacelles, and it featured a bubble cockpit canopy to accommodate the pilot and co-pilot as well as a Plexiglas nose section for the bombardier/navigator. The XB-46 measured 105 feet 9 in (32.23 meters) long with a wingspan of 113 feet (34.44 meters), a height of 27 feet 11 in (8.51 meters), a wing area of 1,285 square feet (119.4 square meters), an empty weight of 48,018 lb (21,781 kg), a gross weight of 91,000 lb (41,277 kg), and a maximum speed of 545 mph (877 km/h); the production version was to be armed with two 0.50-caliber Browning machine guns in the tail and carry 22,000 lb (10,000 kg), with power to be provided by four General Electric J47 turbojets. During the course of developing the XB-46, Convair worked on a forward swept wing attack aircraft project, the XA-44 (redesignated XB-53 in 1946), and the end of the World War II caused severe defense budget cuts, putting Convair in a tight financial bind with regards to the XA-44/XB-53 and XB-46 programs. Facing a tight budget, Convair urged the US Army Air Force to cancel the second and third XB-46 prototypes to save money for the XB-53, and the USAAF agreed to this request in June 1946. (The XB-53 program was cancelled in December 1946 due to concerns about the ability of the forward-swept wing to endure aerodynamic loads at high speed.) The first XB-46 was eventually completed as a stripped-down airframe devoid of armament or military equipment, and it made its first flight on April 2, 1947. A total of 14 test flights at Muroc Army Air Field were conducted until September, after which the XB-46 was used for variety of tests such as noise measurements and tail vibration investigations, with additional stability and control tests being performed at West Palm Beach Air Force Base in Florida from August 1948 to August 1949. After an additional 44 flight hours, the XB-46 was taken out of service due to high maintenance costs and a lack of spare parts, and eventually flown to Eglin Air Force Base where its pneumatic system was tested in cold weather conditions from July to November 1950. The nose section of the sole XB-46 prototype was sent to the Air Force Museum at Wright-Patterson Air Force Base, but the remainder of the aircraft was scrapped in February 1952.

A B-45A Tornado (serial number 47-025) dropping bombs in flight

Even before the XB-45 had made its first flight, on August 2, 1946, the USAAF decided that the XB-45 was superior to the XB-46 because it determined that the XB-46 would be inferior in performance to the XB-45 design and that the slender fuselage of the Convair design would be unable to accommodate the required radar equipment. Therefore, a production order was placed for 96 B-45As and one static test airframe (serial numbers 47-001/097), with the company designation NA-147 used for the B-45A. The B-45A featured improved ejection seats for the pilot and co-pilot, safer emergency exits for the bombardier/navigator and the tail gunner, along with provisions for an E-4 automatic pilot, a bombing navigation radar, and an A-1 fire control system were provided. The first B-45A flew on February 24, 1948, and the first 22 B-45As (deliveries of which began in April) had four Allison J35s, while the remaining B-45As were powered by four General Electric J47 turbojets. Although designed to use a remote-controlled fire control system for the tail gun turret, the B-45As were fitted with a tail gunner's position because of the unavailability of the remote-controlled fire control system. The B-45B was to be a B-45A variant fitted with new radar and fire-control systems, but was not built. The B-45A reached operational USAF units at Barksdale Air Force Base in Louisiana in November 1948, but the B-45A fleet was plagued by maintenance problems with the J47 engines and APQ-24 bombing/navigation radar system, several structural weaknesses in the airframes, difficulties with the gyrocompass at high speed and the E-4 automatic pilot when the bomb doors opened, the lack of suitable bombsights or fire control bombing equipment, and inadequate ferry range and combat radius. Despite these problems, the B-45A found a role as a tactical bomber to deter a Soviet attack on western Europe in the wake of the outbreak the Korean War when the US Air Force in December 1950 initiated the Backbreaker program to fit several B-45As with improved bombing/navigation systems and the Norden bombsight, bomb bays to accommodate lightweight tactical nuclear bombs, and additional electronic equipment, and nuclear-capable B-45As were deployed to the UK beginning in May 1952. As the 1950s progressed, the B-45As were retired from US Air Force service and replaced by the B-47 and also the Douglas B-66 Destroyer tactical bomber, and by July 1958, all B-45As stationed in the UK were relocated to bases in mainland Europe and North Africa, many of them being retired there and broken up for scrap. Some J35-powered B-45As were used for training purposes and designated TB-45A, a few of them serving a target tugs for a Chance Vought target drone glider. On the other hand, one B-45A was modified for use as a launch platform for guided weapons and designated DB-45A, while the last production B-45A (serial number 47-096) was used as an in-flight engine testbed and designated JB-45A.

Left: A classic aerial view of the first B-45C Tornado (serial number 48-001)
Right: An RB-45C Tornado (serial number 48-037)

In September 1947, North American envisaged a variant of the Tornado that could be refueled in midair, the B-45C (company designation NA-153). Although similar to late-production B-45As in having four General Electric J47 turbojets, it differed in having a pair of 1,200-gallon wing tip fuel tanks that could be dropped in flight when necessary, a strengthened cockpit canopy with several reinforcements, a boom receptacle on the top of the fuselage for refueling, and a single-point ground refueling receptacle on the left side of the bomb bays. A total of 43 B-45Cs (serial numbers 48-001/043) were ordered, and the first aircraft flew on May 3, 1949, but by 1950 the US Air Force had decided to place huge orders for the B-47 Stratojet, so the last B-45C to be built in bomber configuration was completed on April 13, 1950. The remaining 33 B-45Cs on order (48-011/043) were completed as reconnaissance aircraft under the designation RB-45C. Unlike the B-45C, the RB-45C had the transparent nose section replaced by a duckbill-shaped nose housing a forward oblique spy camera, and it could carry at least 10 spy cameras (four in the rear fuselage, four at the split vertical section, one tri-metrogen K-17C in a pallet aft of the wing's trailing edge, and one forward oblique camera in the nose) but also 25 M-122 photoflash bombs in the bomb bay. The RB-45C first flew in April 1950, and deliveries of the RB-45C to Strategic Air Command began in June 1950, continuing until October 1951. The RB-45C conducted its first-ever reconnaissance flights over North Korea during the Korean War in the fall of 1950, and for several months the RB-45Cs of the 91st Strategic Reconnaissance Wing were able to evade MiG jet fighters, but after a couple of incidents on 1951 in which the RB-45Cs narrowly escaped interception by MiGs, all RB-45Cs were restricted from overflights of North Korea in daylight operations and converted for night reconnaissance operations in January 1952, receiving black paint to evade interception by enemy searchlights. However, night operations of the RB-45C went awry because the aircraft buffeted badly when the forward bomb bays door opened to release photoflash bombs, and the RB-45Cs were thus withdrawn from use in the Korean War. When the RB-47E reconnaissance version of the B-47 became operational, the RB-45Cs in Air Force service were transferred to the 19th Tactical Reconnaissance Squadron stationed in Europe, with which they served until their retirement in the spring of 1958. The Royal Air Force also used the RB-45C, and four aircraft were leased to RAF crews as part of Operation Ju-jitsu to form the Special Duties Flight, which was headed by Squadron Leader John Crampton and stationed at RAF Sculthorpe in Norfolk, eastern England. The most prolific reconnaissance mission to be carried out by the Special Duties Flight was on April 17, 1952, when three RB-45Cs overflew Kiev from RAF bases in West Germany to obtain intelligence about Soviet military strength; despite being intercepted by Soviet fighters, the RB-45Cs survived and returned to West Germany, and this flight was to serve as a wake-up call for the USSR to reform its air defense systems by making the PVO Strany a branch of the Soviet armed forces independent of the Soviet Army and VVS in 1954. The RB-45C would remain in service until 1959, when it was replaced by the RB-47E and other new-generation reconnaissance aircraft. In the meantime, one B-45C were modified for use as a guided weapons launch platform and designated DB-45C, while the ninth B-45C (serial number 48-009) served as a testbed for the Pratt & Whitney J57 and J75 turbojets under the designated JB-45C. 

Although the B-45 Tornado wasn't as prolific as the better-known B-47 Stratojet given its limitations as a strategic bomber and ended up serving mainly as a reconnaissance platform, its significance was not lost on the fact that it was the first American multi-engine jet bomber to enter service and also the third multi-engine jet bomber to fly, after the Junkers Ju 287 forward-swept wing jet bomber and the Arado Ar 234C four-engine tactical bomber. On the other hand, the XB-46's ability to carry required military equipment was compromised by its fuselage design despite having very high-aspect ratio wings. Like the earlier Douglas XB-43 Jetmaster, the Tornado inadvertently cemented southern California's role as the birthplace of the jet bomber in the United States, but in due time the swept-wing B-47 emerged as the true jet-powered successor to the B-17 and B-29, making clear once again that swept wings were the key for new-generation US bomber aircraft to attain high subsonic speeds.

References:

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

Frederiksen, J.C., 2009. The B-45 Tornado: An Operational History of the First American Jet Bomber. Jefferson, NC: McFarland. ISBN 978-0-7864-4278-2.

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

Would-be aerial combat masters from Santa Monica: the Douglas XB-42 Mixmaster and XB-43 Jetmaster

During World War II, the Douglas Aircraft Company manufactured thousands of its A-20 Havoc and A-26 Invader medium bomber/close air support aircraft from its factories in Long Beach, Santa Monica and El Segundo, and the A-20 Havoc became widely used by the US Army Air Force and Royal Air Force (which referred to the A-20 as the Boston), while the A-26 Invader (redesignated B-26 after 1948) saw action in the last years of World War II and most notably in the Korean War, Bay of Pigs invasion, Vietnam War, Biafra conflict, and the war against the Simba rebels in the Congo. In the last two years of World War II, however, Douglas also came with two one-of-a-kind bomber aircraft, an unorthodox pusher-engine long-range medium bomber and one of America's first-ever jet bomber designs. Because the XB-42 and XB-43 shared the same design except in the powerplant, I've opted to dedicate this post to discussing the design, development, and testing of these two prototype bomber aircraft created from the manufacturing halls Santa Monica.

Models of the XB-42 Mixmaster and XB-43 Jetmaster at the Lyon Air Museum (photographed by me in November 2021)

In early 1943, Douglas investigated the feasibility of a twin-engine close air support aircraft able to carry 2,000 lb (907 kg) of bombs over a combat radius of 2,000 miles (3,219 km) at speeds exceeding 400 miles per hour (643 km/h), and its designer, Ed Burton, believed that these goals could be attained by having the engines buried in the fuselage and coming up with a completely clean wing. By late April, the Model 459 design emerged which had a bug-eye canopy configuration created by a pair of  bubble canopies, two Allison V-1710 liquid-cooled V-cylinder piston engines buried inside the fuselage behind the pilot's cabin that drove two three-bladed counter-rotating propellers in the extreme tail cone via five lengths of shafting, a ventral vertical stabilizer to prevent the propellers from hitting the ground during nose-high takeoffs and landings, a tricycle undercarriage, and an extremely clean laminar-flow wing at the middle fuselage. Armament comprised six 0.50-caliber machine guns, of which four were housed in two remote-controlled turrets on the trailing edges of the wings between the ailerons and flap, and two were mounted in fixed positions on the sides of the fuselage, but also 8,000 lb (3,628 kg) of bombs. A crew of three was carried, of which the pilot and co-pilot/gunner sat under the twin bubble canopies and the navigator/bombardier sat in a transparent nose. The Model 459 was submitted to the US Army Air Force on June 15, and ten days later two prototypes (serial numbers 43-50224/50225) and a static test airframe were ordered under the designation XA-42. A full-scale mock-up was inspected in September, but by this time the Army Air Force regarded the XA-42 as more of a high-speed long-range bomber than a pure close air support plane, and on November 26 the designation of the Model 459 was changed to XB-42, while the name Mixmaster was applied to the XB-42 because the propellers of the aircraft were reminiscent of the Sunbeam Mixmaster electric kitchen mixer.

Top: First XB-42 Mixmaster prototype (43-50224) in flight
Bottom left: XB-42A during taxi tests
Bottom right: Second XB-42 prototype (43-50225)

The first XB-42 prototype was completed in early 1944, only several months after the XB-42 prototype contract had been signed. It made its first flight at Palm Springs Army Air Field on May 6, with test pilot Bob Brush at the controls, and the second XB-42 flew for the first time on August 1. Performance of the XB-42 during initial flight testing was judged to be outstanding, with speed within a percent of that predicted, and the range and climb rate surpassing expectations. However, the twin bubble canopies were found to inhibit poor communication between the pilot and co-pilot/gunner, so the second XB-42 was later fitted with a more conventional cockpit canopy. In the meantime, test flights of the XB-42 revealed a number of problems, including excessive yaw, propeller vibration, and poor engine cooling, and cruciform nature of the XB-42's horizontal and vertical stabilizers required careful handling during taxiing, take-off, and landing due to limited ground clearance. In any case, the XB-42 was not ordered into production, largely because the onset of the jet age ensured that the XB-42 would be last wartime American piston-engine bomber to reach the design phase, but the XB-42 prototypes continued to fly after the end of the World War II for a number of test purposes. The second XB-42 prototype set a new transcontinental speed record in early December 1945 when it flew from Long Beach, California, to Bolling Army Air Field (renamed Bolling AFB in 1948) in Washington, D.C., at a speed of 433 mph (698 km/h). However, on December 16, it was destroyed in a crash at Oxon Hill, Maryland, while on a routine test flight out of Bolling Army Air Field due to a landing gear extension problem, failure of the left engine, and cooling problems with the right engine, and the crew bailed out of the aircraft safely. In the meantime, the first XB-42 prototype was fitted with two auxiliary Westinghouse J30 turbojets under the wings in accordance with an earlier proposal by Douglas to use this aircraft as a turbojet testbed and redesignated XB-42A, making its first flight in this iteration on May 27, 1947. All guns were removed during the conversion process and the XB-42A attained a speed of 488 mph (785 km/h) during its flight testing at Muroc Air Force Base (later Edwards AFB), making a total of 22 flights until late 1947, when it suffered damage to the lower vertical and horizontal stabilizers and rudder after a hard landing. The XB-42A was repaired but was never flew again, and the US Air Force officially removed the aircraft from its inventory on June 30, 1949. The XB-42A was transferred to the collection of the National Air and Space Museum in Washington, D.C. shortly afterwards, only to be later donated to the National Air Museum Storage Facility in Park Ridge, Illinois years later. In April 1959, the fuselage of the XB-42A was moved to storage at the Paul Garber restoration facility at Suitland, Maryland, where it languished until 2010 when it was transferred to the USAF Museum at Wright-Patterson Air Force Base in Dayton, Ohio, for eventual restoration.

Left: First XB-43 Jetmaster prototype (44-61508) taking off for a test flight at Muroc Army Air Field
Right: Color photo of the second XB-43 prototype (44-61509) taking off. The second XB-43 was also called the YB-43 

Even before the XB-42's first flight, in October 1943 Douglas proposed a jet-powered derivative of the XB-42 Mixmaster with two Allison J35 turbojets in the forward fuselage bays, the XB-43 Jetmaster. Besides jet propulsion, the XB-43 differed from the XB-42 in eliminating the ventral vertical stabilizer, ensuring better ground clearance during taxiing and takeoff, but also a larger upper vertical stabilizer to enable adequate longitudinal stability. Two XB-43 prototypes (serial numbers 44-61508/61509) were ordered on March 31, 1944, and to save time and money Douglas decided to use the sole XB-42 static test airframe on order in the construction of the first XB-43 prototype, while the second XB-43 was manufactured from scratch. However, the slowdown in aircraft manufacturing in southern California following the end of World War II and delays in delivery of the J35s due to teething troubles during bench tests meant that the first XB-43 did not fly until May 17, 1946, when it became the first-ever US jet bomber to fly. Months before the XB-43's first flight Douglas discussed with the US Army Air Force plans for an initial production run of 50 B-43s, and it also submitted a proposal to make preparations for the manufacture of 200 aircraft a month. The production aircraft would have a conventional cockpit canopy and a tail turret with two 0.50-caliber machine guns, and two variants were contemplated, the bomber version with a transparent nose and a 6,000 lb (2,722 kg) bombload, and an attack aircraft variant armed with sixteen forward-firing 0.50-caliber machine guns with an unglazed nose and thirty-five 5-inch rockets. However, production plans were axed on August 18, 1945, because the US Army Air Force was now concentrating on its first generation of multi-engine jet bomber, including the North American B-45 Tornado, Convair XB-46, Boeing B-47 Stratojet, Martin XB-48, and Northrop YB-49. The second XB-43, meanwhile, was completed with a conventional canopy and a plywood nose cover, and first flew on May 15, 1947, by which it bore the designation YB-43. Nearly a year into flight tests, in April 1948 the YB-43 (nicknamed "Versatile II" by US Air Force personnel) became one of several testbeds for the General Electric J47 turbojet when it had one of the J35s replaced by a J47. The first Jetmaster prototype was eventually cannibalized to provide spare parts for the YB-43 after that aircraft was damaged during a flight in February 1951, and it was eventually destroyed during target practice at Edwards Air Force Base. The YB-43 continued to fly until December 1953, when it was retired and put in storage at the Paul Garber facility of the National Air and Space Museum the following year pending restoration work. Like the first XB-42 prototype, the YB-43 was transferred to the USAF Museum at Wright-Patterson Air Force Base in Dayton, Ohio, for eventual restoration in 2010.

Artist's conception of the Douglas DC-8 (aka Model 1004) airliner derivative of the XB-42 Mixmaster fast bomber

As a side note, in late 1945 Douglas proposed an airliner derivative of the XB-42, the DC-8 (not to be confused with the later DC-8 jet airliner), to replace the venerable DC-3 on short- and medium-range routes. Known by the company designation Model 1004, the DC-8 would have been 77 feet 8 in (23.67 meters) long with a wingspan of 110 feet 2 in (33.58 meters), a height of 26 feet 9.75 in (8.17 meters), an empty weight of 24,415 lb (11,074 kg), a gross weight of 40,000 lb (18,144 kg), and seating capacity for 40 to 48 passengers in a pressurized cabin. The V-1710s would be located below and immediately behind the cockpit, driving counter-rotating propellers via driveshafts under the cabin floor (which were also proposed for the Douglas Cloudster II prototype light aircraft). The engine arrangement for this aircraft at first glance would have been an unfamiliar spectacle for airport personnel and passengers alike, but was estimated to reduce drag by 30% and eliminate problems associated with controlling the aircraft with one engine out, while cabin access would have been made through single portside door on the sides of the rear fuselage. Despite its estimated performance being greater than that of conventional twin-engine airliners, the DC-8 project itself was shelved in favor of the less risky Convair Model 240 and Martin 2-0-2 airliners due to high complexity and development costs combined with projected high operating costs.

Although the XB-42 and XB-43 remained at the prototype stage only, the Jetmaster itself provided a wealth of aerodynamic data that would be applied to the development of the first American multi-engine jet bombers, including the B-45 and B-47, effectively making the US the first of the major victorious Allies to get a jet bomber into the sky. Moreover, by a stroke of luck, the first XB-42 and the second XB-43 were spared from the breaker's torch and made their way to museums in preparation for restoration to static display, with the hope that someday visitors to the Air Force Museum in Dayton, Ohio will get a rare glimpse of the first-ever US jet bomber in person.

References:

Boyne, W., 1973. "The First, The Last, And The Only: The Douglas XB-42/42A/43". Airpower 3 (5): 13–14.

Francillon, R., 1988. McDonnell Douglas Aircraft Since 1920: Volume I. Annapolis, MD: Naval Institute Press.

Wagner, R., 2004. American Combat Planes of the 20th Century: A Comprehensive Reference. Reno, Nevada: Jack Bacon & Co.