It was formed just prior to the Second World War and intended to provide a reserve pool of manpower to supplement the Territorial Force.

The National Military Reserve was disbanded and most of the constituent units were transferred to the Territorial Force.

Recruits were designated into three classes:[1][2] With the out break of war on 3 September 1939, the National Military Reserve was activated.

[4] The Territorial force itself was stood down in 1943 and by April 1944 all the former National Military Reserve units had been disbanded.

[6] A total of 21 independent infantry companies were formed, of which 12 were disbanded on 1 January 1942, and the remainder transferred to the territorial force on 2 February 1942[7] A total of 22 infantry battalions were formed and were transferred to the territorial force on 2 February 1942[6]