The Thor missile was developed and built by the Douglas Aircraft Company using an engine produced by the Rocketdyne Division.
The guidance system was the responsibility of the AC Spark Plug Division of General Motors.
It was to carry a 1.44MT warhead (the W-49, already used in a number of weapon systems) inside a Mk2 RV (re-entry vehicle) manufactured by General Electric.
As it would require air transportation to its launch sites, the final design had to fit inside a C-124 Globemaster transport aircraft.
The retro rockets were to ensure a clean separation of missile & warhead prior to re-entry
The destruct collar would not be fitted to operational missiles
Thor test launches began on the 25th January 1957 but didn't go well.
The first missile rose only a few centimetres before falling back and exploding.
The second launch in April 1957 would have been a success. However, it was destroyed in flight by the Range Safety Officer whose instrumentation showed the missile to be 180º off course. Unfortunately, his instrumentation was 180º in error and the missile was, in fact, behaving perfectly. The Officer was apparently speedily posted to Alaska!
The third attempt in May 1957 failed when the missile exploded four minutes before launch due to overpressure in a fuel tank.
After 90secs, the fourth launch in August 1957, suffered a technical problem and was destroyed from the ground.
A Thor missile explodes on the launch pad and another whilst in flight
Finally, on the 20th September 1957 (only a few weeks later than planned) Thor achieved it's first 'full range flight' - a great achievement considering the problems experienced and the problems with funding.