Scrambler telephone handset for privacy unit (later known as Secraphone), c.1941, first developed for government and military use as a secure telephone system and issued by the General Post Office (GPO) in the UK around 1937.

British Prime Minister Winston Churchill used this telephone system, later known as Secraphone, during the Second World War for secret communications within the British government and military. This scrambler telephone was first developed for government and military use as a secure telephone system and issued by the General Post Office (GPO) in the UK around 1937.

This telephone set was used in combination with a large external box known as a privacy unit, of which we have an early and insecure example in our collections - 2004-184 Privacy set 6AA (GPTN) Diagram SA 5061. The privacy unit used electronic circuits and radio valves to scramble outgoing telephone calls and unscramble incoming calls. Early privacy units suffered from reliability and security problems and could only deter a casual listener. The design was improved and made more secure later in the war.

During World War II, most of the scrambler telephones sets were manufactured by Telephone Manufacturing Company (TMC) and Plessey. Later post-war commercial versions were known as Secraphone, to which all examples of the handset are now commonly referred.