The Provisional IRA which was the larger, dominant faction from 1972 onward, and the more violent/active group, was not Communist or Marxist-Leninist. The Official IRA which was the main Communist/Marxist Leninist began in 1969 and declared a ceasefire in 1972, the last attack it had on the British Army in 1975. It is true that the Provisional IRA called itself Democratic Socialist but they almost universally had no analysis or understanding of socialism and would work it out after Independence