Supersonic Low Altitude Missile The Supersonic Low Altitude Missile or SLAM ( not to be confused with the U . S . Navy ' s current " Standoff Land Attack Missile " ) was a canceled U . S . Air Force project conceived around 1955 . Although it never proceeded beyond the initial design and testing phase before being declared obsolete , it represented several radical innovations in tactical aircraft . The SLAM was designed to complement the doctrine of mutually assured destruction , and as a possible replacement for or augment to the Strategic Air Command system . In the event of nuclear war it was intended to fly below the cover of enemy radar at supersonic speeds , and deliver thermonuclear warhead s to roughly 16 targets . The primary innovation was the engine of the aircraft , which was developed under the aegis of a separate project code - named Project Pluto , after the Roman god of the underworld . It was a ramjet that used nuclear fission to superheat incoming air instead of chemical fuel . Project Pluto produced two working prototypes of this engine , the Tory - IIA and the Tory - IIC , which were successfully tested in the Nevada desert . Special ceramic s had to be developed to meet the stringent weight and tremendous heat tolerances demanded of the SLAM ' s reactor . These were developed by the Coors Porcelain Company . The reactor itself was designed at the Lawrence Radiation Laboratory . The use of a nuclear engine in the airframe promised to give the missile staggering and unprecedented low - altitude range , estimated to be roughly ( over four and a half times the equatorial circumference of the earth ) . The engine also acted as a secondary weapon for the missile : direct neutron radiation from the virtually unshielded reactor would sicken , injure , and / or kill living things beneath the flight path ; the stream of fallout left in its wake would poison enemy territory ; and its strategically selected crash site would receive intense radioactive contamination . In addition , the sonic waves given off by its passage would damage ground installations . Another revolutionary aspect of the SLAM was its reliance on automation . It would have the mission of a long - range bomber , but would be completely unmanned : accepting radioed commands up to its failsafe point , whereafter it would rely on a Terrain Contour Matching ( TERCOM ) radar system to navigate to preprogrammed targets . Although a prototype of the airframe was never constructed , the SLAM was to be a wingless , fin - guided aircraft . Apart from the ventral ram - air intake it was very much in keeping with traditional missile design . Its estimated airspeed at thirty thousand feet was Mach 4 . 2 . The SLAM program was scrapped on July 1 , 1964 . By this time serious questions about its safety had been raised , such as how to test a device that would emit copious amounts of radioactive exhaust from its unshielded reactor core in flight , as well as its efficacy and cost . ICBM s promised swifter delivery to targets , and because of their speed ( the Thor traveled at roughly Mach 12 ) and trajectory were considered virtually unstoppable . The SLAM was also being outpaced by advances in defensive ground radar , which threatened to render its stratagem of low - altitude evasion ineffective . Reactor design . The reactor had outer diameter of 57 . 25 in and length 64 . 24 in ; the dimension of the reactor core was 47 . 24 in diameter and 50 . 70 in length . The critical mass of uranium was 59 . 90 kg , and the reactor ' s power density averaged at 10 megawatts / cubic foot , with total power of 600 megawatts . The nuclear fuel elements were made of refractory ceramic based on beryllium oxide , with enriched uranium dioxide as fuel and small amount of zirconium dioxide for structural stability . The fuel elements were hollow hexagonal tubes about 4 in long with 0 . 3 in distance between the outer parallel planes , with inside diameter of 0 . 227 in . They were manufactured by high - pressure extruding of the green compact , then sintering almost to its theoretical density . The core consisted of 465000 individual elements stacked to form 27000 airflow channels ; the design with small unattached elements reduced problems related with thermal stress es . The elements were designed for average operation temperature of 2330 °F ( 1277 °C ) ; the autoignition point of the reactor base plates was only 150 °C higher . The neutron flux was calculated to be 9×10 neutrons / cm . s in the aft and 7×10 neutrons / cm . s in the nose . The gamma radiation level was fairly high due to the lack of shielding ; radiation hardening for the guidance electronics had to be designed . The reactors were successfully tested at Jackass Flats of the Nevada Test Site . The Tory II - A reactor , the scaled - down variant , was tested in mid - 1961 and successfully ran for several seconds on May 14 , 1961 . A full - scale variant , the Tory II - C , was run for nearly five minutes at full power . The latter test , limited by the air storage facility capacity , ran for 292 seconds . The air fed to the reactor was preheated to 943 °F and compressed to 316 psi , to simulate ramjet flight conditions .