The No. 4 Mk 1 was officially adopted by Britain as the primary military service rifle, replacing the No.1 series of rifles.
The rifles just prior to the No.4 and just after the No.1 Mk III were intermediate rifles. The first being the SMLE Mk V rifle in 1922 followed by the No.1 Mk VI in 1926. In 1931 the No.1 Mk VI was modified and became the No.4 Mk 1. Although developed very early the No.4 was not released to the British Army as the primary battle weapon until 1939.
The No. 4 Mk 2, Mk 1/2, and Mk 1/3 had their triggers pivoted to the receiver instead of the trigger guard.
The No. 4 rifle was manufactured in Britain, Canada, Pakistan, and the U.S.
