On a spring evening in 1987, eight members of one of the IRA’s most formidable rural units were cut down in a British Army ambush in Loughgall, County Armagh. It was the single deadliest day for the IRA during the post-partition conflict colloquially known as “the Troubles”—a turning point in what republicans called the long war against British rule in the North.

Nearly four decades later, the ambush that wiped out the East Tyrone Brigade’s elite unit remains cloaked in secrecy, with repeated attempts by the British state to block a public inquiry. How British forces acquired such precise operational intelligence is still the subject of unanswered questions—and deep suspicion within Republican circles.

The deaths of the eight Volunteers marked more than a tactical defeat. It was the destruction of a unit widely seen as the cutting edg ...