An E-4B Nightwatch aircraft flies over the U.S. Navy Blue Angels F-18s during the 2009 Defenders of Freedom Open House and Air Show, Aug. 29 – 30, 2009. (U.S. Air Force/Josh Plueger)

The U.S. Air Force is delaying the official solicitation for its E-4B Nightwatch replacement, citing a new acquisition strategy approach.

In an update last week, the service said it recently classified its Survivable Airborne Operations Center, or SAOC, Weapon System program -- intended to replace the infamous nuclear command-and control aircraft commonly known as the "Doomsday" plane -- as an Acquisition Category 1D program.


That category covers major procurements, typically costing billions of dollars. The "D" classification requires a defense acquisition executive, who reports to the defense or deputy defense secretary, to oversee the program.


Because of the change, the request for proposal "originally planned for release in December 2020 is delayed," according to the presolicitation notice. The service said additional timeline details would be forthcoming.

Last December, Congress authorized $16.6 million for the SAOC's research and development.

The Air Force and the Navy -- which oversees the E-6B Mercury fleet, a companion aircraft to the E-4B -- want to consolidate the two aircraft's missions.

The E-4B, also known as the National Airborne Operations Center, can be used by the president and defense secretary to execute operations in the event of a nuclear war; the E-6B "looking glass" aircraft serves as an airborne communications relay between the Pentagon's National Command Authority and U.S. nuclear submarine, bomber and missile forces.

The Navy keeps 16 E-6B aircraft, which are based on a commercial Boeing 707 and began flying in the early 1990s. The Air Force has four E-4Bs, which are modified versions of the Boeing 747 and have been in service since the 1970s.

Traditionally used by defense secretaries for transport around the world, the aging Nightwatch had to ditch that secondary mission because too many E-4Bs required maintenance, according to a report from DefenseOne. The website noted that the E-4B and the two planes used by the president are among the oldest 747-200s still flying.

Small fleets are a drain on the service because they drive up operational costs, according to a 2019 report, "The Air Force of the Future: A Comparison of Alternative Force Structures," by Todd Harrison, director of the Aerospace Security Project at the Center for Strategic and International Studies.

"[The problem] that the Air Force has right now, which is making its operating costs so much higher, is because they have so many small fleets," he said.

The E-4B was built to withstand an electromagnetic pulse in the event of a nuclear blast. The Air Force is hoping for the same hardened architecture in its replacement.

"In case of national emergency or destruction of ground command control centers, the SAOC aircraft will provide a highly survivable command, control and communications platform to direct US forces, execute emergency war orders, and coordinate actions by civil authorities," according to the service's initial notice, posted last December.

This article originally appeared on Military.com. Follow @militarydotcom on Twitter.