Martin B-57 Canberra

B-57 Canberra
Martin B-57A USAF 52-1418.jpg
B-57A in flight over Chesapeake Bay, Maryland
RoleTactical bomber
ManufacturerMartin
First flight20 July 1953[1]
Introduction1954
Retired1983 (USAF)
1985 (Pakistan)
StatusRetired from military service; 3 in use by NASA[2]
Primary usersUnited States Air Force
Pakistan Air Force
Republic of China Air Force
Number built403
Unit cost
US$1.26 million (B-57B)[3]
Developed fromEnglish Electric Canberra
VariantsMartin RB-57D Canberra
Developed intoMartin/General Dynamics RB-57F Canberra

The Martin B-57 Canberra is an American-built, twinjet tactical bomber and reconnaissance aircraft that entered service with the United States Air Force (USAF) in 1953. The B-57 is a license-built version of the British English Electric Canberra, manufactured by the Glenn L. Martin Company. Initial Martin-build models were virtually identical to their British-built counterparts; Martin later modified the design to incorporate larger quantities of US-sourced components and produced the aircraft in several different variants.

The B-57 Canberra holds the distinction of being the first jet bomber in U.S. service to drop bombs during combat.[4] The Canberra was used extensively during the Vietnam War in a bombing capacity; dedicated versions of the type were also produced and served as high-altitude aerial reconnaissance platforms (the Martin RB-57D Canberra), and as electronic warfare aircraft. The B-57 Canberra was also sold to export customers abroad; further combat use was seen by the Pakistani Air Force during the Indo-Pakistani War of 1965 and the Indo-Pakistani War of 1971.

In 1983, the USAF opted to retire the type; the B-57 Canberra's retirement marked the ending of the era of the tactical bomber. The three remaining flightworthy WB-57Fs are technically assigned to the NASA Johnson Space Center, next to Ellington Field in Houston, as high-altitude scientific research aircraft,[2] but are also used for testing and communications in the U.S. and Afghanistan.[5]

Development

Origins

At the outbreak of the Korean War in 1950, the USAF found itself in dire need of an all-weather interdiction aircraft. The existing inventory of piston-engined Douglas B-26 Invaders had been dispatched in this capacity at the very start of the conflict; however, within only a few months within the theatre, the B-26 had suffered a very high rate of attrition and successes with the type were typically limited.[1] In response to these needs, the USAF requested the British government to provide a private demonstration of the English Electric Canberra, a newly developed jet-powered bomber. On 17 August 1950, the Canberra demonstration was performed at RAF Burtonwood, Warrington, Cheshire, England; during the following month, a team of US test pilots and engineers visited English Electric's Warton factory to perform a series of flight tests and a detailed technical assessment of the aircraft.[1]

On 16 September 1950, the USAF formally issued a request for a jet-powered bomber; the sought aircraft had to possess a top speed of 630 mph (1,020 km/h), ceiling of 40,000 feet (12,190 m), and range of 1,150 miles (1,850 km). Full all-weather capability and a secondary reconnaissance role also had to be included in the design. The American contenders included the Martin XB-51, the North American B-45 Tornado and AJ Savage.[1] To expedite the process, only projects based on existing aircraft were considered and, unusually, the service considered foreign aircraft. These included the Canadian Avro Canada CF-100 and the British English Electric Canberra, which had not yet officially entered service with the Royal Air Force (RAF).[1] Aviation authors Bill Gunston and Peter Gilchrist commented that "It seems likely that this first batch of trials convinced the Americans that the Canberra was ideal for the job, but in order to satisfy the US Senate a competitive evaluation of all likely contenders had to be arranged".[1]

As part of the USAF evaluation's process, all five aircraft were submitted to a series of fly-offs to determine their performance. On 21 February 1951, a British Canberra B.2 (WD932), flown by Roland Beamont, made the transatlantic journey, arriving in the United States to participate in the competition; by making this journey, the Canberra thus became the first jet aircraft to perform a non-stop unrefueled flight across the Atlantic Ocean, travelling from Warton, England, to Gander, Newfoundland and Labrador, Canada, in the record time of 4 hours 37 minutes.[1] On 26 February 1951, the flyoff took place at Andrews Field, Prince George's County, Maryland; each aircraft was tasked with performing a set sequence of maneuvers within a ten-minute window, directly demonstrating its agility and performance against its rivals. According to Gunston and Gilchrist, the Canberra proved to be significantly superior to any of the competing aircraft, and its selection was beyond doubt by the end of the competition.[1]

Production arrangements

That the Canberra was a foreign aircraft meant its superiority in terms of performance did not guarantee political support in spite of the urgent need, particularly in light of there being several rival indigenous aircraft designs. There were also doubts about production availability with English Electric being able to mesh with USAF demands, as well as questions over continued spares support.[1] In March 1951, many of these questions were answered; with production lines already at full capacity meeting Royal Air Force orders and those emerging from other export customers, English Electric entered into discussions with Glenn L. Martin Company. It was proposed that Martin would receive a license to domestically build the Canberra in the United States. According to Gunston and Gilchrist, the Americanization of the Canberra program proved effective at dismissing much of the political opposition to the project.[1]

The British-built Canberra B.2 that was used as a pattern and prototype for the B-57

On 23 March 1951, the USAF issued a contract to Martin, requesting the manufacturing of an initial quantity of 250 Canberras, which had received the USAF designation B-57A (Martin internally designated the type as the Model 272).[1] On 3 April 1951, English Electric and Martin both signed a formal licensing agreement to cover the Canberra's production.[1]

During August 1951, a second British-built Canberra (WD940) was flown to the US to act as a pattern aircraft for Martin, as well as to perform assorted trials and to support performance validation of airframe changes.[6] On 21 December 1951, one of the British pattern aircraft (WD932) was lost in accident; although this was subsequently discovered to be caused by incorrect fuel scheduling having led to the tail-heavy aircraft exceeding its design limits during a maneuver, the crash jeopardized the entire program and invigorated the anti-Canberra political opposition.[6] The crash did lead to some design changes in the face of political pressure, but these were not implemented on the first 75 aircraft to be produced.[6]

Due to the great urgency placed on delivering the B-57A Canberra, the initial phase of manufacturing performed by Martin used a minimum-change formula to expedite production; thus the first B-57As to be produced were largely identical to the Canberra B.2.[1] As such, more than 30 changes that had been requested by the Wright Air Development Center (WADC) were rejected on program schedule or cost grounds.[6] One noticeable exception was the adoption of more powerful Armstrong Siddeley Sapphire engines capable of producing 7,200 lbf (32 kN) of thrust, which were license-built in the United States as the Wright J65. The Sapphire-based J65 powerplant had been selected in place of the British-built Canberra's Rolls-Royce Avons as the USAF had placed an emphasis on operations within hot climates and intended to fly at a slightly higher maximum gross weight than the RAF's operating practices.[7]

Several other minor differences were also present between early US-built and UK-built Canberras. These changes included the canopy and fuselage windows being slightly revised, the crew being reduced from three to two, the adoption of wingtip fuel tanks, engine nacelles were modified with additional cooling scoops, and the conventional "clamshell" bomb bay doors were replaced with a low-drag rotating door originally designed for the XB-51.[8] As a result of these changes, the bomb bay of the US-built aircraft was slightly smaller than its UK-built counterparts in order to allow the American aircraft to carry more fuel; however, the overall external shape of the Canberra remained unchanged.[6]

In early July 1953, the first US-built production aircraft (52-1418) rolled out; it conducted its maiden flight on 20 July 1953.[6] One month later, this initial production aircraft was accepted by the USAF, by which point a cessation of hostilities had come into effect in Korea. This was one of only eight B-57A Canberras to be manufactured; the remaining 67 aircraft from this first batch, deemed no longer to be required as bombers, were converted on the assembly line to serve as medium-altitude reconnaissance aircraft while retaining all the basic Canberra features, and were accordingly re-designated as the RB-57A Canberra.[6]

Further development

B-57B Canberras of the 345th Bombardment Wing in flight, 1957

In place of the curtailed B-57A, a more refined bomber variant, the B-57B, was developed. Having a more lengthy development time, this model incorporated the structural and system changes that had been recommended by WADC, which resulted in the aircraft being more adaptable than its B-57A predecessor.[6] Of the external changes, the most significant was the adoption of a fighter-style canopy accompanied by a flat-panel windshield and a tandem seating arrangement, providing for greater transparency and an improved view for both the pilot and navigator, as well as allowing for a gunsight to be equipped. The corresponding glazed bombing nose of the B-57A was deleted along with the starboard crew entrance to the cockpit.[9]

The B-57B introduced several other major changes. In terms of armaments, a total of four hardpoints attached to the outer wing panels were installed on this variant, capable of mounting external bombs and rockets. The B-57B was also furnished with a gun armament for strafing attacks. The first 90 aircraft to be produced were equipped with a total of eight 0.50 cal (12.7 mm) Browning machine guns installed within the wings; on later aircraft these were substituted for by an arrangement of four 20 mm M39 cannon.[10] A new rotary bomb door was adopted on the B-57B, which had originally been designed for the XB-51, replacing the hinged doors; this proved to be faster to open/close and reduced buffeting, which in turn improved accuracy and allowed for faster attack speeds. The redesigned bomb bay also enabled faster turnaround times on the ground.[11]

In addition, hydraulically-operated triangular air brakes were installed on the rear fuselage, which worked in addition to the existing 'finger'-type brakes installed in the wings; the new brakes gave the pilots a greater level of controllability, improving the accuracy of low-level bombing runs.[10] The B-57B was equipped with an APW-11 Bombing Air Radar Guidance System for target approach guidance, as well as a APS-54 radar warning receiver.[12] The engines were also furnished with a new cartridge starting system, eliminating the reliance on ground start carts.[12]

The substantial design changes between the B-57A and B-57B models resulted in delays to the overall program, as well as incurring substantial costs on the fixed-price contract. Gunston and Gilchrist stated of the consequences to the program: "This was clearly not the manufacturer's fault, but the money effectively ran out after 177 of the planned 250-aircraft order had been completed".[12] In 1954, in response to the sound performance offered by the B-57B, the USAF elected to place a large second order; this included a further 100 B-57B bombers, 38 B-57C trainers, and 20 RB-57D high-altitude reconnaissance aircraft.[12] In 1955, a final batch of 68 B-57E target tugs was ordered.[12]

In 1969, in response to demands for a capable night interdiction aircraft for combat operations in the Vietnam theatre, a total of 16 B-57B Canberras were substantially rebuilt during a lengthy upgrade program.[13] These aircraft received an entirely new nose section containing an AN/ANQ-139 forward-looking radar, a low-light television system, and an AN/AAS-26 forward-looking infrared detector. A laser rangefinder/designator was also installed, and the wing pylons modified to accommodate laser-guided Paveway bombs, while all the guns were removed to save weight.[14] During the production run from 1953 to 1957, a total of 403 B-57s were built.

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