Under the terms of the Military Training Act 1939, all male British subjects aged between 20 and 21 were liable for call up for a year's training in the armed forces. Those so called up were known as Militiamen. Provision was made for postponement of liability in hardship cases, for the establishment of tribunals for conscientious objectors and for safeguarding reinstatement in civil employment.
Following the outbreak of the Second World War, the Military Training Act 1939 was superseded by the National Service (Armed Forces) Act 1939, which imposed a liability to service with the armed forces on men aged between 18 and 41 years.
The Military Recruitment Department was set up in 1939, under the aegis of the Director-General of Manpower, to administer these National Service Acts. These were further extended in 1941 by the National Service Act 1941, which extended the liability to service in civil defence, and the National Service (No 2) Act 1941, which imposed on all persons of either sex a general obligation to service in the armed forces, civil defence or industry and extended the upper age limit of liability to service in the armed forces to 51 years.
The detailed execution of the Acts was carried out locally through the National Service Officers under the guidance of the Department. All men and women liable for conscription were registered at employment exchanges or other employment offices, medically examined, and issued with directions appropriate to their required military duties. Medical Boards, whose responsibilities were enlarged at the start of the War to include volunteers as well as conscripts, were administered with the assistance of the Ministry of Health, under the provisions of the 1939 Military Training Act. The Department was also responsible for dealing with applications for deferment and for the registration of conscientious objectors, whose cases were heard by local and appellate tribunals. It was advised by a Medical Advisory Committee and a Military Service (Hardship) Committee. It was also responsible for dealing with refusals by employers to reinstate servicemen and women in civil employment. At the end of the War it therefore played a major role in military demobilisation and resettlement.
After the War, the Military Recruitment Department took over the remaining work of the National Service Department (which had been set up in 1939 to supervise the national service scheme and the distribution of manpower between the armed forces, civil defence and industry). The National Service Acts 1939 to 1942 continued in force until the end of 1948, when the National Service Act 1948 repealed them and provided for continuing national service in the armed forces for men for a defined period of eighteen months wholetime service and a total period of additional and part-time service of 5½ years. The National Service Act 1950 increased the period of wholetime service to two years. The main functions of the Department continued to involve supervision of registration, medical examination and enlistment, including the deferment of call-up and conscientious objection. After the Suez crisis of 1956 the Department was concerned with the repatriation of British subjects. In 1957 the government decided to phase out national service, which came to an end in 1960. The Department was then subsequently wound up.