Colonel Hugh Anthony Johnstone OBE was the administrative head of SIGINT (Signals Intelligence) in the British Army during the 1970s.

Johnstone became known when he was identified by the magazines Peace News and The Leveller as the much-publicised anonymous witness Colonel B in the ABC Trial in 1978.

Johnstone was commissioned into the Royal Corps of Signals from Sandhurst in 1952. He was promoted to lieutenant in 1954, captain in 1958, major in 1965, lieutenant-colonel in 1970, and colonel in 1975. He retired in 1979.