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 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. (Reporting by Nathan Gomes in Bengaluru; Editing by Shailesh Kuber)