The MI5 during World War I

Abstract

Prior to Britain’s entry into World War I, the British Security Service opted for the close surveillance rather than the immediate arrest of identified German agents to dismantle
the German spy network at the outbreak of war. During the war, counterintelligence relied on the monitoring of incoming and outgoing passengers, letters and telegrams to identify German spies, a practice, which resulted in the capture of enemy agents working with rudimentary methods, including the so-called ‘lemon juice spies’. As German espionage eased from 1916, MI5’s focus shifted from counter-espionage to counter-subversion. Germany sought to undermine the British war effort by inciting
and supporting groups with hostile feelings towards the British Empire, including Irish separatists and Indian revolutionaries. After the October Revolution in Russia, the focus of counter-subversion shifted to eliminating the communist threat.