April 26 (Reuters) - The U.S. Air Force said on Friday

that it has awarded a contract to Sierra Nevada Corp to develop

a successor to the E-4B, known as the Doomsday plane, due to its

ability to survive a nuclear war.

The Survivable Airborne Operations Center (SAOC) project is

intended to replace the aging 1970s-era aircraft, which is

approaching end-of-service life, a Air Force spokesperson said

in a statement.

To satisfy operational requirements, the weapon system will

comprise of a commercial derivative jet hardened and modified to

meet military requirements.

Reuters in December reported that the U.S. Air Force

eliminated Boeing ( BA ) from its competition to develop a

successor to the E-4B Nightwatch.

The Air Force currently operates four E-4B aircraft with at

least one on alert at all times. The fleet of highly-modified

Boeing 747-200 jumbo jets has become increasingly difficult and

expensive to maintain as parts become obsolete.

The E-4B is expected to reach the end of its service life in

the early 2030s.