Martin XB-51

Aircraft Profile
Martin XB-51 landing.
(photo, U.S. Air Force)


As the Cold War heated up between the West and the Soviet Union in the late 1940s, the United States Air Force moved ahead with plans to field a large number of close-support bomber squadrons with a new aircraft model, the Martin B-51 medium bomber. In the end, the urgency to field a jet bomber to replace the ageing A-26 Invader proved to much and the British-designed Canberra bomber was selected for front line use. The XB-51 concept was a radical new design of airplane. It had a swept-wing configuration and a tri-engined appearance – the first of its kind to be incorporated into a military aircraft and years ahead of Boeing’s 727 airliner. The sudden onset of the Korean War spelled the end of the XB-51 program. At the beginning of the war, the US Air Force was in dire need of medium bombers to assist ground troops. The Canberra was the logical selection for them. The British aircraft design was well proven, maneuverable and reliable, and more importantly for the US military, it could be mass produced in short order.

The true history of the XB-51 program can be traced back to the Douglas A-26 Invader close-support bomber that performed so well in combat in the closing stages of World War II. In the immediate post war years, the US Army Air Force, decided it needed a replacement plane to tackle possible Soviet tank columns attacking over the central plains of Europe. Three major companies submitted designs and specification bids for the new plane. At the end of the evaluation process, the design submitted by the Martin Company was rewarded with the contract, under the designation XA-45. In May 1946 two prototypes were ordered under the new designaton of XB-51. However, in the spring of 1946, the United States Air Force sent out a revised requirement for a medium close-support bomber with more emphasis on speed and less on load-carrying. The big and heavy XB-51 design could not meet these new requirements and so in February 1947 Martin submitted a new design. This was accepted by the USAAF and a radical new XB-51 was born.

Almost every component that was selected to be incorporated in the new bomber was advanced. Aside from the already mentioned swept wing design and its tri-jet configuration, the XB-51 was to employ a rotary weapons bay that would enable the airplane to deliver it’s bombs while flying at high speeds. Something that the newest US bombers, the B-1 Lancer and B-2 Spirit incorporate today. But the real trademark of the XB-51 was speed. The aircraft was designed to outrun almost all of the fighter aircraft of the early 1950s. The XB-51 power plant consisted of three 5,820 lb-thrust General Electric J47 turbojet engines. Aside from these powerful (for the time) engines, the aircraft were designed to be equipped with an additional four 1000 lb-thrust RATO bottles to assist in take-off. With these engines, the airplane reached a top speed of 645 miles per hours. Its cruising speed was 538 mph.

The bomber was manned by a crew of two. The pilot sat beneath a fighter style “bubble” canopy. The second crew member, the navigator/radio-operator, sat behind the pilot. The navigator could only view the sky through a small observation window on the left side of the fuselage. The cockpit was pressurized and temperature conditioned. The XB-51 would have a payload capability of 10,400lbs of ordnance in its internal bomb bay. It was also equipped with eight powerful 20-mm cannons located in the nose of the aircraft. The cannons could fire 1,280 rounds of ammunition before they needed to be reloaded. Operational ceiling for the new aircraft was an amazing 41,400 ft. Another impressive characteristic of the XB-51 was its un-refuelled ferry range of nearly 1,600 miles.

On the morning of the 28th October 1949, the XB-51 first prototype, tail number 46685, took to the air for the first time at Baltimore, Maryland. The plane flew as anticipated by Martin. The Air Force was so impressed with the flight testing of the XB-51 that it ordered Martin to finish work on the other test plane, serialled 46686. As it turned out, they would be the only two B-51s ever to be built. The situation in the Korean Peninsula had taken a turn for the worse in 1950 when Communist North Korean troops invaded the South. The US needed to quickly get into service a modern close-support aircraft for the theater and the only proven design available was that of the English Electric Canberra. The Canberra was chosen by the Air Force on March 1951, and this decision meant the end of Martin’s XB-51 close-support bomber.

The two XB-51 prototypes cost the US government the sum of 12.5 million dollars. Much of their subsequent career was spent at Edwards AFB perfecting the rotary bomb door and performing bomb delivery trials, before piloting accidents ended the lives of both aircraft. Martin, who had to “eat” much of the development cost for aircraft, quickly bounced back with the development and production contracts for the B-57 bomber – the Canberra fitted with the XB-51s rotary bomb door – which went on to become a very successful aircraft. The Panther, the name that the Air Force may have given to the XB-51, was an aircraft born ahead of its time. Many of the remarkable features incorporated in today’s bombers, came directly from the XB-51 program.

Front view – note the large flaps and landing
gear. (photo, U.S. Air Force)
Rear view showing wing & tailplane sweep.
(photo, U.S. Air Force)


Requirement Specification:
Manufacturers Designation: Model 234

Development History:
XA-45 Initial design. 6 crew medium bomber with straight wing, 2 turboprop and 2 jet engines.
XB-51 Revised design. Much smaller 2-seater with three jet engines and swept-wing. 2 prototypes built – initially without fin/tailplane bullet fairing.
XB-51 Proposed version with tandem crew seating under single canopy.
XB-51 Proposed seaplane version with boat hull, hydroskis or hydro-sled landing gear.


Key Dates:
Nov 1944    USAAF issues requirement for new attack aircraft.
Feb 1946    Martin XA-45 selected as winner of competition.
23 May 1946    Two prototypes ordered under new designation of XB-51.
Spring 1946    USAAF issues revised requirements for faster and lighter aircraft.
31 March 1947    USAAF approves new design for XB-51.
4 Sept 1949    XB-51 first prototype officially rolled out.
28 Oct 1949    First flight of first prototype.
4 April 1950    USAF flight testing begins.
17 April 1950    Second prototype makes first flight.
Sept 1950    B-26 Night Intruder replacement requirement issued.
26 Feb 1951    Competitive fly-off between XB-51 and Canberra.
6 March 1951    Canberra selected by USAF.
14 June 1951    USAF issues RBL-X requirement for daylight tactical bomber.
29 Nov 1951    Douglas B-66 selected to meet RBL-X.
Nov 1951    XB-51 production plans cancelled.
8 Dec 1951    XB-51 officially enters USAF service.
28 Feb 1952    First prototype damaged in landing accident.
9 May 1952    Second prototype lost when maneuvering at low altitude.
28 Feb 1953    First prototype returned to service for bomb delivery testing.
1955    XB-51 appears in the movie ‘Towards the Unknown’.
25 March 1956    First prototype lost in take-off accident.
The red nose pitot was only fitted to 46-0685.
(photo, U.S. Air Force)
Elegant view of the first prototype.
(photo, U.S. Air Force)


Military Operators

U.S. Air Force (prototypes only)

Government Agencies


Civilian Operators



Martin XB-51
Crew: Two – Pilot and Navigator
Dimensions: Length 85 ft 1.25 in (25.94 m); Height 17 ft 3 in (5.26 m); Wing Span 53 ft 1.25 in (16.19 m); Wing Area 548.00 sq ft (50.91 sq m).
Engines: Three General Electric J47-GE-3 or -17 turbojets, rated at 5,820 lb st (25.89 kN) for take-off with water injection, plus for RATO bottles rated at 1,000 lb (4.45 kN) thrust, fitted as necessary.
Weights: Empty Equipped 29,584 lb (13,419 kg); Normal Take-off (‘combat’) 41,457 lb (18,804 kg) for basic attack mission; Maximum Take-off 62,452 lb (28,328 kg).
Armament: Eight 20 mm (0.787 in) cannon in nose with 1,280 rnds total; 10,400 lb (4,717 kg) maximum of bombs or 8 x 5-in High Velocity Aerial Rockets (HVAR) in internal bomb bay.
Performance: Maximum level speed 645 mph (1038 km/h) at sea level, 598 mph (962 km/h) at altitude at maximum take-off weight; Cruising speed 538 mph (866 km/h); Initial rate of climb 5,100 ft/min (1554 m/min); Service ceiling 41,400 ft (12,619 m); Combat radius 595 mls (958 km).
XB-51 in landing configuration.
(photo, U.S. Air Force)
XB-51 46-0685 in flight.
(photo, U.S. Air Force)


Design Centre

Head of Design Team: ?
Programme Manager: ?
Design Office: Glenn L. Martin Company, Middle River, Baltimore, Maryland.


(Glenn L. Martin Company, Middle River, Baltimore, Maryland, USA.)
Version Quantity Assembly Location Time Period
XB-51 2 Middle River, MA Apr 1949-Apr 1950
Total: 2    

Total Produced: 2 a/c

Production List

To be added.

Both Martin XB-51s.
(photo, U.S. Air Force)
The first XB-51 in flight.
(photo, U.S. Air Force)

More Information


‘The Martin XB-51 – Air Force Legends Number 201’
by Scott Libis
Published by Steve Ginter, 1998 ISBN: 0 942612 00 0
* Very well illustrated monograph

‘Wings of Fame, Volume 14’
Published by Aerospace Publishing, 1999 ISBN: 1 86184 029 2
* Includes ‘Industry of Prototypes’ feature on the XB-51


‘Aircraft Modelworld, Vol. 3 No.10 Dec 1986’
* Includes scale drawings of the XB-51.

‘Airpower, July 1978’
* Includes article on XB-51.

‘Airpower, March 1997’
* Includes article on XB-51.


Martin Model 234

wikipedia: Martin XB-51

Past Military Aircraft: XB-51

Martin XB-51

Gilbert XF-120 (Martin XB-51)

Air Force Museum Factsheet: Martin XB-51


Flight Simulator Models:
To be added.

Scale Models:
To be added.

Scale Drawings:
See Aircraft Modelworld article above.


To be added.