The Rocketdyne division of North American Aviation developed a relatively small liquid-fuelled rocket engine for thrust augmentation of manned aircraft during the late 1950s.

[1] The variable-thrust AR2 is a direct development of the fixed thrust AR1, which was given the military designation LR36.

The AR2-3 had variable-thrust and single lever throttle control, regulating flow of oxidiser to the turbo-pump gas-generator and thus flow of propellants to the combustion chamber.

[1] Initial flight trials were carried out attached to the belly of North American F-86F-30-NA Sabre (52-4608 / FU-608) re-designated F-86F(R), boosting performance to a top speed of M1.22 at 60,000 ft (18,288 m).

[2] The AR2-3 was evaluated in 1999 as part of the Future-X Demonstrator Engine project, for possible use in the Boeing X-37 Reusable Upper Stage Vehicle at a thrust of 6,600 lbf (29.34 kN), with a specific impulse of 245 seconds.