The flying wing story goes back to the early 1940s when Jack Northrop's company obtained military funding to further his dream of creating an all-wing aircraft. The N-1M made its first flight on July 3rd 1940, from Muroc Dry Lake in California. Northrop was contracted to build four N-9M aircraft to serve as subscale prototypes for the USAAF's upcoming XB-35 flying wing bomber.

The XB-35 made its first flight on June 25th, 1946, powered by four Pratt & Whitney 3000hp R-4360 engines, each fitted with two contra-rotating propellors. There were problems with the R-4360, and two YB-35s were taken off the Northrop production line to be finished as YB-49s, with eight turbojet engines. The Air Force cancelled the B-35 program in November 1949.

The first YB-49 made its maiden flight on October 21st 1947, from Muroc Dry Lake. It was not a true flying wing, as it featured four vertical stabilisers and four ventral fins for increased stability. The second example flew on January 13th 1949. On June 5th 1948, this aircraft crashed, killing its entire crew. The first YB-49 was written off in a high-speed taxying accident on March 15th 1950.

A third YB-35 was converted to a six-jet configuration as the YRB-49A. This made its maiden flight on May 4th 1950. Ultimately this failed to meet USAF requirements, as had the eight-jet YB-49, and was scrapped. It was not until the appearance of low-observable technology for military aircraft that the flying wing concept would re-appear.

The technology to build a low-observable aircraft started to become practical in the mid-1970s. Lockheed flew the XST in 1977, and in 1978 received a contract to build an operational "stealth fighter", designed to carry out precise, covert attacks on high-value targets in any theatre.

At the time that the XST flew, Strategic Air Command's bomber plans were in a state of flux. In June 1977, B-1 production had been halted by the Carter Administration in favour of the cruise missile, apparently leaving the Air Force without a modern penetrating bomber for the 1980s and beyond. At about the same time, strategic analysts in the Pentagon started looking at a whole range of new weapons systems. The most radical of these emerged from a program called Saber Penetrator, which assumed that the B-52 or other aircraft would be available as a cruise missile launcher and called for a new bomber designed specifically to penetrate Soviet airspace. It was to use the most advanced technology available and need not be in service until 1990.

By 1981 it was becoming obvious that the US really did need a new long-range multi-role aircraft, and an upgraded B-1 was the only serious contender. On October 20th 1981, President Reagan announced that 100 B-1Bs were to be built, with IOC sometime in 1986. This would coincide with the B-52 being relegated to a stand-off cruise missile carrier and allow the Advanced Technology Bomber to develop in a less urgent atmosphere.

There were two competing designs submitted in the Advanced Technology Bomber competition. Northrop's "Senior Ice" was in competition with Lockheed's "Senior Peg", basically a scaled-up F-117 with four engines and two crew. "Aurora" was one of the code names for this competition.

Northrop was awarded a $9.4bn contract to develop the ATB on November 4th 1981. This contract covered five Engineering, Manufacturing and Development (EMD) airframes, one airframe for static-test and one fatigue article. The idea was for this aircraft to enter service in the 1990s and replace the B-1B as a penetrator, and the B-1s would, in turn, replace B-52s as cruise missile launchers.

Tacit Blue, a low-observable technology demonstrator, made its first flight in February 1982 and went on to log 134 more flights over a three-year period. This basically proved that a manned low-observable surveillance aircraft with a low-probability-of-intercept radar and other sensors could operate close to the forward line of battle without being detected. Tacit Blue provided valuable engineering data that aided the design of the B-2. The program was declassified on April 30th 1996.

Development of the ATB proceeded in almost complete secrecy. Unclassified information amounted to the fact that Northrop, Boeing, Vought and General Electric were the main contractors, 132 were to be built, and the aircraft incorporated low-observable technology.

Although program costs were kept secret, they kept rising. In 1984 a change to the wing center section to allow the aircraft to penetrate at a low level cost $1bn directly and probably incurred extra costs by the delay it caused to the rest of the program.

In April 1988, the US Air Force released an artist's impression of the B-2 (see image, left). With the exception of the engine exhausts, it was more accurate than most people realised.

The first B-2, 82-1066, was rolled out at Palmdale, California, on November 16th 1988. It made its first flight on July 17th 1989.

On December 16th 1988, USAF Secretary Aldridge announced that the ATB program cost had increased by 16% to $42.5bn in 1981 dollars or $68.1bn in "then-year" dollars. This meant that each aircraft would cost about $516m. These figures were based on a very optimistic production schedule.

The Air Force believed that it needed the B-2 to be able to locate and destroy mobile Soviet ICBMs such as the SS-24 and SS-25. However, the collapse of the Soviet Union and the end of the Cold War in 1991 made this mission largely redundant. Reductions in B-2 production were inevitable.

In 1991, procurement was cut from 132 to 75, and then even further to 15. It was later raised to 20, giving the USAF just enough aircraft for a 2-squadron Wing. Not surprisingly, the cost of each B-2 rocketed to over $1bn, or more than twice that if R&D; expenditure is included. A total of $44.4bn was spent on developing and producing the B-2.

On May 6th 1992, Northrop Grumman, the B-2 industrial team, and the Air Force were awarded the 1991 Collier Trophy "for the greatest achievement in aeronautics or astronautics in America demonstrated in actual use in 1991." The Collier Trophy is awarded annually by the National Aeronautic Association and is widely considered to be the most prestigious aviation award in the United States.