The competing PGM-19 Jupiter missile saw more use, but both were quickly eclipsed by the Air Force's long range ICBM program, which could be fired from U.S. soil.

By 1959, with the Atlas rocket well on its way to operational status, both Thor and Jupiter programs became obsolete as delivery vehicles, yet continued to be built and deployed until 1963 for political reasons and to maintain aerospace industry employment.

The program proceeded quickly as a stop-gap measure, and within three years of inception the first of 20 Royal Air Force Thor squadrons became operational in the UK.

One of the advantages of the design was that, unlike the Jupiter MRBM, the Thor could be carried by the USAF's cargo aircraft of the time, which made its deployment more rapid.

[citation needed] A small number of Thors with "Thrust Augmented Delta" boosters and W-49 Mod 6 warheads remained operational in the anti-satellite missile role as Program 437 until April 1975.

Early Thor engines suffered from foaming turbopump lubricating oil at high altitudes and bearing retention issues, resulting in several launch failures.

It was erected at LC-17B and underwent several practice propellant loading/unloading exercises, a static firing test, and a month-long delay while a defective relay was replaced.

The booster performed normally, but the flight was terminated at 35 seconds after an erroneous console readout caused the Range Safety Officer to believe that the missile was headed inland instead of out to sea.

Missile 104, launched 22 August from the newly opened LC-17A, broke up at T+92 seconds due to a drop in signal strength from the programmer, causing the engine to gimbal hard right.

The Jupiter, Thor, and Atlas missiles all used a variant of the Rocketdyne LR-79 engine and all three suffered launch failures due to a marginal turbopump design.

In contrast, the USAF's General Schreiver rejected the idea of sending Thor and Atlas missiles back to the factory so as to not delay the testing program.

Five successful Thor tests were conducted in June–July 1958, the last one carrying a mouse named Wickie on a biological mission; the capsule sank into the ocean and could not be recovered.

On 30 July 1958, six Douglas technicians were severely burned, three fatally, when a LOX valve failed at the Thor static test stand in Sacramento, California.

Nonetheless, Thor was declared operational and testing now began at Vandenberg Air Force Base on the West Coast when Missile 151 flew successfully on 16 December.

After Thor 203 repeated the same failure four weeks later, an investigation found that the culprit was a safety wire that had been meant to prevent the control tape in the programmer from inadvertently coming loose during vehicle assembly.

The wire would ordinarily be cut after installation of the programmer in the missile, but Douglas technicians had forgotten this important step, thus the tape could not be spooled and the pitch and roll sequence did not activate.

The Jupiter missile, a joint effort of Chrysler and the Redstone Arsenal in Huntsville, Alabama, was originally designed to attack high-value targets like airfields, train switching yards and command and control sites with extremely high accuracy.

With two IRBMs of nearly identical capabilities, it seemed obvious that only one of the two would ultimately achieve operational status, resulting in a competition between the Army and Air Force.

Accidents such as the explosion of Thor 103 were avoided, and the turbopump issues that plagued early Rocketdyne engines were also resolved in Jupiter much earlier than the Air Force's missiles.

The Jupiter program was more successful due to far better testing and preparation, with each missile given a full duration static firing in Huntsville prior to delivery.

A static firing stand for Thor tests was only opened in May 1958, at which point the missile's launch record stood at four successes and nine failures, including four launchpad explosions.

Thanks to the thorough testing done at Huntsville, Jupiter missiles mostly all arrived at CCAS in flight-ready condition while Thors typically required extensive repairs or modification before launch.

After the Soviet launches of Sputnik 1 and 2 in late 1957, U.S. Secretary of Defense Charles Wilson announced that both Thor and Jupiter would go into service as his final act before leaving office.

Deployment of the IRBM fleet to Europe proved more difficult than expected, as no NATO members other than the UK accepted the offer to have Thor missiles stationed on their soil.

Thor was deployed to the UK starting in August 1958, operated by 20 squadrons of RAF Bomber Command under US-UK dual key control.

The entire launch sequence, from starting to roll back the missile shelter through to ignition of the rocket engine and lift-off, took approximately 15 minutes.

Due to its mysterious nature, appearing at a very high altitude and being visible for hundreds of miles, the cloud attracted widespread attention and was published by the news media.

[6][7] Prof. James MacDonald at the University of Arizona Institute for Atmospheric Physics investigated the phenomena and linked it to the Thor rocket launch after contacting military personnel at Vandenberg Air Force Base.

When the launch records were later declassified, the United States Air Force released a memo explaining that the cloud was "the result of a military operation", but did not clarify.