On 25 July 1953, Mac Stíofáin took part in an IRA arms raid on the armoury of the Officers' Training Corps at Felsted School in Essex.
While incarcerated in Wormwood Scrubs and Brixton prisons, he learned not only a smattering of Greek from the Cypriot EOKA prisoners (he befriended Nikos Sampson) but also "the realities of an anti-British rule guerrilla campaign" [REF].