SNC E-4C Survivable Airborne Operations Center. The E-4C Survivable Airborne Operations Center (SAOC) is a United States Air Force program to develop a replacement for the E-4B National Airborne Operations Center (NAOC), a strategic command-and-control military aircraft used as a mobile command post for the National Command Authority in emergency situations. 

The current E-4 platforms were built in the 1970s. The airframes are reaching the end of their operational lifespans and support costs are increasing. Because of this, in 2019, the USAF began a program to develop a new platform. This program will take several years to complete. The E-4s will continue to fulfill the role in the meantime.

Sierra Nevada Corporation was selected to develop the aircraft. The company announced that the aircraft will be based on 747-8i and will be collaborating with Rolls Royce.

Development 

The program began in 2019. The age issues regarding the E-4 platform were recognized much earlier. In 2006, then-Defense Secretary Donald Rumsfeld attempted to retire the aircraft due to its age, with the first plane scheduled for retirement in 2009.

In 2007, with no capable replacement, Rumsfeld's successor, Robert Gates, overturned the decision and kept all the planes in the fleet. The E-4B airframe has a usable life of 115,000 hours and 30,000 cycles, which will be reached in 2039. The maintenance limiting point will occur sometime in the 2020s.

Like the B-21 Raider, the USAF expects to take advantage of off-the-shelf commercial products and digital design to a greater degree than in previous projects, to streamline development and reduce acquisition costs by relying less on bespoke components.

Operational status is not expected until the 2030s. In March 2023, USAF Gen. Thomas Bussiere testified to the United States House of Representatives Armed Services Committee that "the SAOC will achieve FOC (full operating capability) in the early to mid-2030s." A US Senate report on the FY2024 National Defense Authorization Act (NDAA) includes a section on the SAOC wherein the Armed Services Committee "encourages the Secretary to maintain the current recapitalization schedule in order to replace the aging fleet and field the more capable aircraft by the 2032 required assets available date."

In August 2023, Sierra Nevada Corporation (SNC) announced the construction of large  maintenance, repair, and overhaul hangars in Dayton, Ohio, as a part of their bid for the SAOC contract. SNC released renderings of the hangars with Boeing 747-8s in them, indicating that the 747-8 is the likely platform for the SAOC.

In August 2024, the project received the designation E-4C.

Funding 
Since the FY2021 NDAA, Congress has appropriated nearly $300 million in development funds, including $76.4 million for the first contracts in 2021. The Air Force requested substantially greater funding in FY2024, asking for $888.8 million. As of the FY2024 funding request, the program is expected to cost $8.3 billion between FY2022 to FY2028.

Selection process 
As of August 2023, Sierra Nevada Corporation (SNC) was reported to be bidding for the contract, on a platform assumed to entail data and communication modifications to a number of used 747-8 airframes.

In December 2023, Boeing was eliminated from the bidding process, after refusing to give up data rights to the 747-8, leaving SNC unopposed in the selection process.

In April 2024, Sierra Nevada Corporation was awarded a $13 billion contract for five aircraft with the contract expected to be completed by 2036. In May 2024, Sierra Nevada announced the purchase of five Boeing 747-8s from Korean Air for conversion, to be delivered for modification work by September 2025.

Design 
Details about the design have not been publicly released, partially due to the classified nature of its mission but also because the project is still in development. The Air Force described its mission in the FY2024 budget request:The Survivable Airborne Operations Center (SAOC) will replace the aging E-4B fleet which faces capability gaps, diminishing manufacturing sources, increased maintenance costs, and parts obsolescence as it approaches the end of its serviceable life. SAOC will provide POTUS, SECDEF and the CJCS a worldwide, survivable, and enduring node of the National Military Command System (NMCS) to fulfill national security requirements throughout all stages of conflict. As a command, control and communications center directing US forces, executing emergency war orders and coordinating the activities of civil authorities including national contingency plans, this capability ensures continuity of operations and continuity of government as required in a national emergency or after negation/destruction of ground command and control centers. SAOC will fulfill the requirements of the AF Nuclear Mission by providing Nuclear Command, Control and Communications (NC3) capabilities to enable the exercise of authority and direction by the President to command and control US military nuclear weapons operations.

While the project is in the early stages as of 2023, some of the existing project work has set requirements that would seem to rule out any aircraft platform except the Boeing 747-8. In 2022, Col. Brian Golden said:
You need a very large, four-engine aircraft to execute our mission set. There was a lot of discussion on: Could it be done on two engines? Partly. A lot of risk would have to be taken, and it wasn’t the Air Force’s risk to take.

This statement seems to strongly suggest that the Air Force will once again turn to the Boeing 747, the only US-made four-engine airliner built in the several years prior, and the only aircraft based on a four-engine airliner platform built in the US since the last new-build E-3 Sentry and E-6 Mercury aircraft, both based on the Boeing 707 platform, were delivered in 1991. The only other four-engine airliner in recent construction is the Airbus A380, but production for that ended in 2021. The Air Force is generally reluctant to use aircraft not built in the United States, especially for highly sensitive missions such as the SAOC will take on.

While 747-8 production ended in January 2023, the Air Force has left open the possibility of purchasing used aircraft. Col. Golden said that a new aircraft wouldn't be necessary, making acquisition of a used 747-8 a possibility.
You don’t have to buy a brand-new aircraft. It’s not like a car... You can buy an older aircraft—a few years old, five years old, it doesn’t matter—and the engineers will strip it down and build it back up.

The FY2024 budget justification includes an expectation that the contractor will "buy the required aircraft, bring each aircraft to a common configuration, make required modifications, develop and integrate the mission system into each aircraft, provide required ground support systems and conduct contract support operations for fielded systems until Operations and Support Phase."

The Defense Department has looked at the possibility of merging the capabilities of the US Navy's Boeing E-6 Mercury, currently the only aircraft with nuclear command-and-control capabilities, into the SAOC so that the roles of both the E-4B and the E-6 are handled by one aircraft. This would also address the age of the Boeing 707 platform upon which the E-6 is based, which first flew in the 1950s. However, the Navy has chosen to replace the E-6 Mercury with the E-130J. The new platform will continue the E-6's TACAMO mission but will drop the ICBM command-and-control capabilities of the E-6. Those capabilities will be integrated into the SAOC.

Planned capabilities have not been publicly discussed in great detail, but the program requirements include:
 Aerial refueling capability to enable sustained airborne operations
 Hardening against electromagnetic pulse (EMP) and nuclear effects
 Nuclear Command, Control, and Communications (NC3) capabilities
 Secure communications and planning capabilities based on a Modular Open System Approach (MOSA)

Technological enhancements and capabilities 
The SNC E-4C Survivable Airborne Operations Center (SAOC) is designed to incorporate advanced technologies that enhance its operational capabilities in various scenarios. One significant feature is its hardening against electromagnetic pulse (EMP) effects, which ensures that critical systems remain operational even after a nuclear event. This capability is crucial for maintaining command and control during national emergencies. Additionally, the SAOC will include secure communication systems and air refueling capabilities, allowing it to operate for extended periods without needing to land, thereby increasing its effectiveness as a mobile command center.

See also

References 

Aircraft
Aviation
United States Air Force