Shortly after the start of the Korean War in June, 1950, the USAF’s Strategic Air Command (SAC), led by then-Lt. Gen. Curtis LeMay, implemented a plan to deploy new Boeing B-50 atomic-bomb-capable strategic bombers to Canada (in 1950 the US had only fission nuclear weapons; thermonuclear fusion weapons–the “hydrogen bomb”–did not yet exist).
From Winning Armageddon, by Trevor Albertson (more here), p. 37, relating to July 10 from the “Papers of Curtis E. LeMay”:
…In the Goose Bay [Canada] area would be the 43rd Bomb Group with 40 tankers at Goose and one Bomb Squadron, and two Bomb Squadrons at Harmon Field [Canada (west coast of Newfoundland)]. They would operate against Leningrad from Goose and land in the North African theatre for future operations…
The following paragraphs are based on the book U.S. Nuclear Weapons in Canada, by John Clearwater and an article at The Bulletin of the Atomic Scientists. Only a very few people in the Canadian government at first knew of the planned deployment, which was approved (without knowledge of the intended target, one is pretty sure). The full cabinet was informed on August 18. It is not clear if the nuclear weapons aspect was considered then. At the end of the month the USAF deployed its planes to Canada. Eleven atomic bombs were stored in a nearby forest (the article says 15, see pp. 3-4 PDF for the full episode); as far as I can determine these were the implosion bomb casings with high explosive, but without the fissionable plutonium “pits” that turned them into actual nuclear weapons, more here on implosion bombs. Those pits were kept separately under US civilian control at that time. The article states: “another secret operation involved the transfer of non-nuclear components to Canada in July and August of 1950.”
In November the bombers returned to the US. More from the article:
While transporting one of the Mark IVs [atomic bombs] back to the United States on November 10, a B-50 bomber experienced trouble over Canadian territory. First one engine failed and then a second began to backfire. With little hope of reaching a u.s. base, standard procedure called for the bomb assembly to be jettisoned over water. Fuzes were set to detonate at an altitude of 2,500 feet and the bomb was dropped in the middle of the 12-mile wide St. Lawrence River, not far from Riviere du Loup, Quebec. The explosion of the Mark IV’s nearly 5,000 pounds of chemical high explosive frightened residents and rattled windows up and down the river. The air force used a cover story to explain the blast-the facts did not emerge until four decades later…
The first overseas movement of nuclear components-capsules [i.e. pits]-came in 1951…
The Canadian government was not best pleased about the explosion, as you can read in the link to Mr Clearwater’s book.
Mark Collins
Twitter: @Mark3Ds
Mark Collins 3Ds Blog 
The “Armageddon” book above stresses LeMay’s claim that he needed to go first in a pre-emptive nuclear strike by SAC against Soviet bombers and their airfields to prevent a terribly damaging attack by the USSR vs the US.
Before the U-2 became operational in 1956 did the US have significantly detailed intelligence (e.g. through SIGINT) on the locations of Soviet strategic nuclear assets to make such a pre-emptive attack feasible? Or was LeMay just providing cover for what would have in fact been basically a counter-value strike against Soviet cities and industrial capabilities as opposed to a counter-force one?
1) U-2 history: https://www.lockheedmartin.com/en-us/news/features/history/u2.html
2) This from a former CIA director suggests strongly that before 1956 LeMay would not have targeting data need for a successful pre-emptive strike vs. Soviet nuclear forces: https://www.lockheedmartin.com/en-us/news/features/history/u2.html
Mark Collins
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Was fissile material actually stored in Canada?
Mark Collins
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