In the 1970′s Martin Marietta hoped to follow up the X-24A and X-24B with the X-24C. Vaguely similar to the X-24B in shape, it would be an all-new rocket powered hypersonic lifting body research vehicle. Air launched from under the wing of a B-52, the X-24C could be equipped with a number of experimental modules, including internal weapons bays (to test the dynamics of weapon ejection at hypersonic speeds) to scramjet engines.
Lockheed studied a very similar series of vehicles, also (unofficially) calling them “X-24C.” None were built ?
