The SR-71 Blackbird was retired by the United States Air Force in 1998,[2] eliminating a unique and useful intelligence, surveillance and reconnaissance (ISR) capability.

[3] The first unconfirmed reports about the SR-72 appeared in 2007, when various sources said Lockheed Martin was developing an airplane able to fly six times the speed of sound or Mach 6 (4,000 mph; 6,400 km/h; 3,500 kn) for the Air Force[4][5]—about twice as fast as the SR-71.

[10] Company officials announced plans to build an optionally piloted scaled demonstrator that would be 60 ft (18 m) long, about the size of a Lockheed Martin F-22 Raptor, and powered by one full-scale engine to fly for several minutes at Mach 6; it would be ready in 2018 for flight testing that would follow the timeline for the hypersonic High Speed Strike Weapon.

[6][2] On 13 November 2013, Air Force Chief of Staff General Mark Welsh said the service was interested in hypersonic flight, which would reduce the time an adversary would have to react to an operation.

Pressed by budget cuts, the service chose instead to develop the Northrop Grumman RQ-180 stealth UAV—expected to be cheaper and less complex to design and manufacture—to conduct ISR missions in contested airspace.

[12] In December 2014, NASA awarded Lockheed Martin a contract to study the feasibility of building the SR-72's propulsion system using existing turbine engine technologies, The $892,292 (~$1.13 million in 2023) contract funded a design study to determine the viability of a TBCC propulsion system by combining one of several current turbine engines, with a very low Mach ignition Dual Mode Ramjet (DMRJ).

NASA previously funded a Lockheed Martin study that found speeds up to Mach 7 could be achieved with a dual-mode engine combining turbine and ramjet technologies.

[9] The two firms were reported to be collaborating on turbine-based combined cycle (TBCC) propulsion system, with plans to begin developing the SR-72 hypersonic demonstrator in 2018, with the first flight expected in 2023.

"[20] In January 2018, Lockheed Vice President Jack O'Banion gave a presentation that credited the advancements in additive manufacturing and computer modeling, stating that it would not have been possible to make the airplane five years ago and that 3D printing allowed a cooling system to be embedded in the engine.

[21][22] In February 2018, Orlando Carvalho, executive vice president of aeronautics at Lockheed Martin, pushed back on reports of the SR-72's development, saying that no SR-72 had been produced.