To conserve resources in training, the British and Australian Army converted many .303 rifles to .22 calibre for target practice and training purposes after the First World War. In 1926, the British government changed the nomenclature of its rifles, designating the .303 calibre SMLE as No. 1 Rifles and the .22 calibre training rifles as No. 2 Rifles. For practical purposes "SMLE" and "No. 1 Rifle" are alternate names for the same weapon, but a purist would define a No. 1 as post-1926 production only.

Subcaliber .22 Rifles

For the most part the early sub caliber rifles were made from converting regular rifles into training rifles. There were Long (Lng .22) and Short (Sht .22) this designation referred to the length of the barrel. Most of the conversions involved replacing the .303 barrel with a new .22 cal barrel but some barrels were bored out and sleeved. Later .22 cal rifles were made based on the No4 receiver, these were the C No7 MkI, No7 MkI, No8 MkI, and No9 MkI. The C No7 MkI was manufactured in Canada, this rifle was not a conversion but actually built as a .22 cal trainer. The magazine was fitted with a loading ramp and the rifle was a single shot. The British No7 MkI was made by converting No4 rifles by sleeving the old barrel or by replacing the barrel. The magazine for these rifles was fitted with a small 5 round .22 magazine welded inside so the rifle would work as a repeater. The next .22 cal rifle was the No8 MkI, this rifle was designed more as a target rifle. It did not have the full wood like the previous rifles and there is no magazine, a fully adjustable trigger was also fitted. A final batch of .22 trainers was made and designated the No9 MkI, these were again conversions of the No4 rifles and included some Mk1/2 and Mk2 rifles with the trigger hung from the receiver. These rifles had full wood, and the magazine consisted of a standard .303 mag with the spring and follower removed.