The MI5 During World War II

Abstract

MI5 proved to be vulnerable to Soviet intelligence during World War II, as its focus was primarily on the war with the Third Reich. During the war, a number of Soviet spies infiltrated the British Security Service, the most famous of whom are now known as the Cambridge Five. The MI5’s network of double agents successfully misinformed
German intelligence through a series of covert operations, helping Britain to victory. The Double-Cross System proved effective against the Germans, but the detection and defection of Soviet agents infiltrating MI5 at the start of the Cold War made British intelligence services realise that Russian intelligence had established an extensive network in Britain long before the Soviet Union turned into its enemy after World War II.