by JOSEPH TREVITHICK

During the early years of the Cold War, the United States had a problem.

The U.S. had quickly lost its monopoly on nuclear weapons. The Pentagon was most concerned about Soviet and Chinese weapons, but France was also building a nuclear bomb.

France was — and is — a U.S. ally. But still, it was reason enough for America to send in its spy planes.

In the 1960s, two specially modified KC-135R Stratotankers joined the U.S. Air Force’s 55th Strategic Reconnaissance Wing. The aircraft had special gear to covertly gather data on French detonations in the South Pacific.

“France conducted its nuclear tests … on the Mururoa Atoll in the Tuamotu Archipelago of French Polynesia,” an official Air Force history stated. “Nearly all French nuclear devices were detonated from balloons, but an occasional one was dropped from aircraft.”

The National Security Archive at George Washington University obtained this historical review and other documents via the Freedom of Information Act.

It’s a revealing look at how allies spy … on allies.

American agents had kept an eye on French nuclear aspirations from as early as 1946. With the Cold War underway, Washington worried that the French nuclear program might fall into the wrong hands.

“A reliable source reports that there has been a rumor circulating to the effect that French scientists have the formula and techniques concerning atomic explosives,” Army Lt. Col. S.M. Skinner, a member of the Strategic Services Unit, wrote that year in a memo to the Manhattan Project’s Foreign Intelligence Section.

“They are now willing to sell this information,” Skinner added.

The Strategic Services Unit spun off from the Office of Strategic Services after World War II. The group existed briefly before being absorbed into the new Central Intelligence Agency.

“[Frédéric] Joliot-Curie inspired suspicion because of his communist politics,” Jeffery Richelson, a senior fellow at the National Security Archive, wrote in his book Spying on the Bomb.

Joliot-Curie—among the academics named in Skinner’s note—was a prominent physicist, a member of France’s nuclear research team … and a former member of the Communist National Front resistance group against the Nazis.

On top of that, France had an active Communist party and powerful left-leaning politicians. American officials often butted heads with the country’s more centrist leaders, as well.

And regardless, “any nation’s possession of nuclear weapons and its strategic doctrine governing their use could have an impact on the balance of power in a region, as well as the prospects for crisis resolution and deterrence,” Richelson wrote in an email to War Is Boring.