The mid 1950’s to early sixties were the glory days of American nuclear experimentation. Almost any application of nuclear weapons that could be thought of would be investigated. And not just with a mere concept review. No, the nuclear labs and their affiliates in universities and industry received the funds and personnel to realize their creative visions. That’s what I really think it was in some cases. Pure unfettered creative expression without much concern for real strategic need, or even the limits of material possibility. These people were artists, avant garde composers, poets, all testing the artistic limits of their chosen medium. And from 1955 to 1964, some of them were working on SLAM, the deadliest flying thing ever thought of.
SLAM Was Pure Art:
Most articles you read about the Supersonic Low Altitude Missile (SLAM) will say that SLAM got underway as an actual funded project as a response to the 1957 launch of Sputnik. Others describe SLAM as a reasonable choice according to academic nuclear policy and use language from the late sixties to discuss it. I think these people are wrong. SLAM was an investigation into the limits of the possible done as much for aesthetic reasons as meeting military or political goals. There were already plenty of responses to Sputnik, including the Nautilis taking a trip under the North Pole. And interpreting SLAM in academic language that did not exist at the time is no explanation at all. They tried to make it because they could think it.
SLAM was a proposed nuclear-thermal ramjet driven missile that could stay aloft for months flying at Mach 3 at only 500 feet (150m) off the ground while popping the occasional nuclear weapon out of its back like a toaster. It could also kill with its sonic boom and it would leave a trail of fallout behind from its unshielded reactor. It was literally a flying doomsday machine programmed to fly over the target nation for weeks causing mayhem after delivering its dozen or so bombs.
This is a photo of a model of SLAM on its launcher based on 1964 paintings and drawings. It is not based on any actual missile because SLAM was cancelled in 1964 just as airframe test designs were being built.
I can guess what you are thinking. Nuclear propulsion may be fine for ships and submarines, but reactors are heavy, they don’t seem to belong in an aircraft. You are absolutely right, and that’s not considering safety issues if there’s a crash. But why are reactors so heavy? There are two reasons: pressure containment and radiation shielding. Most nuclear reactors are simply super efficient steam engines that keep their fuel from melting under its own generated heat by keeping the core surrounded by high pressure water in a strong pressure vessel. Some of the water is taken out to drive turbines, then cooled and pumped back into the reactor.
There are alternative reactor designs that can operate at higher temperatures and lower pressures. The Thorium salt reactor at Oak Ridge I discussed a few weeks ago was originally built as a uranium salt reactor to test aircraft propulsion systems. This test reactor was safe, unless you crash, but did not quite have the hoped for power to weight ratio. Other reactor designs were air cooled solid fuel reactors. These could generate far more power in principle, but there were few compounds containing sufficient amounts of fission fuel that would not melt or fracture in the intense heat. Even if these solid fuel systems could hold together, they would disperse fission products into the air behind them. Neither reactor type could be sufficiently shielded to protect aircrews. Nuclear propulsion of aircraft was abandoned in the late 1950s.
But that didn’t stop the dream of nuclear propulsion. What if you made a pilotless cruise missile powered by a nuclear ram jet that could pop bombs out the top like a toaster? The sonic boom and nuclear contamination would be a feature, not a bug, when it it was flying over enemy territory.
In January 1957, months before Sputnik, Project Pluto began their task of building a nuclear ramjet for SLAM. They were surprisingly successful. Here’s a BBC4/Discovery Channel Documentary from a few years back when many of the Pluto team were still alive:
They actually got Tory II-C, the ramjet engine, to work as well as it would need to for SLAM. This video is split into five parts. Part two should come up on the screen when part one ends.
Here’s a picture of II-C, II-A is in the header image:
Why was SLAM Cancelled?
Umm, because it was completely insane, perhaps? Well, that didn’t always stop folks back then, though safety was a major reason Pluto was cancelled in 1964 and all papers from SLAM materials tests transferred to NASA. Notice in the video that the engine had to be handled remotely in a shielded building after each test? And if you built a SLAM, how would you test it? The research staff had to be two miles away and wait for favorable winds just for those short engine tests. A flight test in a real airframe would be incredibly risky and meet with political opposition. And if you even could build a working airframe, there would still be problems with loading weapons onto it Supersonic release at low altitude was still a technical problem that would not be fully solved until the B61 series bombs came along, and SLAM’s toaster launcher would put more stress on a bomb that even a B61 could take.
But perhaps more importantly, the mission capabilities of SLAM were not needed. By 1964 the US was beginning to deploy a highly effective ICBM force that could perform most of SLAM’s missions.
SLAM was cancelled in part because it was not needed. I don’t think it was researched and tested really because of a perceived need. It was the last glorious book length Beat poem or Abstract Expressionist installation in the medium of late fifties nuclear weapons design.