Supersonic Low Altitude Missile

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The Supersonic Low Altitude Missile (SLAM) was a U.S. Air Force project started in the mid-1950s and canceled in 1964. It was designed to be an unmanned, nuclear-powered missile that could fly at supersonic speeds close to the ground to avoid radar and deliver thermonuclear warheads deep into enemy territory.

SLAM would use a nuclear ramjet engine to heat incoming air and push the missile forward. The plan was to have it operate without a crew and rely on automated navigation to hit multiple targets, making use of very low-altitude flight to stay under radar cover. It was meant to complement, or augment, existing strategic forces and potentially replace some bomber missions.

A key part of SLAM was the on-board nuclear propulsion developed under Project Pluto. The engine, tested as Tory-IIA and Tory-II-C prototypes in the Nevada desert, would power the missile at high speed. The airframe was to be wingless and fin-guided, earning the nickname Flying Crowbar. The design also included automatic terrain-following navigation (TERCOM) to reach pre-programmed targets.

The concept promised an extremely long reach and rapid strike capability—an estimated range well over 100,000 miles, with speeds around Mach 4.2 at high altitude. However, the project faced serious questions about testing a vehicle with a nuclear reactor emitting exhaust in flight, its overall viability and cost, and the safety implications. By the early 1960s, advances in intercontinental ballistic missiles and ground radar reduced SLAM’s practicality.

The program was officially canceled on July 1, 1964. In the end, SLAM never progressed beyond design and early testing, but it featured groundbreaking ideas in automated, unmanned nuclear propulsion and low-altitude rapid delivery.

Key facts
- Concept: unmanned, nuclear-powered missile using a ramjet engine
- Project duration: roughly 1955–1964
- Engine: nuclear reactor-powered ramjet developed under Project Pluto (Tory-IIA and Tory-II-C tests)
- Airframe: wingless, fin-guided, nickname Flying Crowbar
- Flight profile: supersonic, very low altitude, automated guidance
- Speed and range: about Mach 4.2; estimated range >100,000 miles
- Cancellation: safety, cost, and the rise of faster ICBMs and radar-guided defenses
- Reactor and fuel: compact ceramic-fuel reactor delivering hundreds of megawatts of power; tests conducted at the Nevada Test Site