The Military Service Act of 27 January 1916 brought conscription into play for the first time in the war. Along with the Defence of the Realm Act, it was possibly the most important piece of legislation in placing Britain onto a “total war” footing. The procedure for calling up the classes of men defined in the Act were laid down in Army Council Instruction 336 of 1916. The procedure was generally the same as that used to call up men from the Groups of the Derby Scheme. This was defined in Army Council Instruction 86 of 1916.
The Groups for single men closed at midnight 1/2 March 1916 and from that time all legally eligible men not exempted were deemed to have passed into the army reserve. It was not necessary to attest these men but their basic details had to be entered on the enrolment form B.2513.
Army Council Instruction 379 reminded Area commanders to provide medical facilities for the examinations necessary to complete enrolment. Men who failed the medical and enrolment were told they would not be needed again; those who passed were told they would have another medical when called up.
Men of Class 1 (that is, 18 year olds), once enrolled, were given the option of returning home or remaining with the Colours and undergoing special training until they were 19. (ACI 839, 18 April 1916)