The censor's stamp

In wartime, the post can be a source of information for the enemy.  Even innocent personal letters can give away information on troop’s positions and battle plans. Grumbles about conditions or other signs of low morale could be exploited by the enemy.

During the First World War, the Post Office was responsible for censoring post from the troops. Censorship took place at base Post Offices at Le Havre and later Boulogne.  The role of the postal censor was also important in catching spies. The Post Office was responsible for the capture of many enemy agents in the UK; partly through their efforts all but one of the German spies operating in Britain during the war were detected, and 14 were executed.

The monitoring and control of telegraphs also became the responsibility of the Post Office. Even before war was declared in August 1914 the Post Office was issued with a warrant permitting it to detain telegraph messages sent to Germany.

Letters to the troops from home had to be addressed only by name, military number and unit, care of the GPO. This stopped information on where soldiers were based being revealed.