When initially introduced the Pistol Case, Royal Armoured Corps had a long strap that allowed it to be worn on the thigh, rather than being positioned at the waist as was more typical with holsters. The idea was that this would be more comfortable for seated men than having it on the waist where it would dig in when sat down. In reality the lengthy stap needed to position the holster on the thigh was more trouble than it was worth as it had a tendency to catch on items within an AFV. The other features of the holster, such as the external channel for the cleaning rod and the loops for spare ammunition were well liked as they meant a separate ammunition pouch was not needed and the single strap made access to the holster easier than a full flap holster. With this in mind the Mk I holster began to be modified from around 1942 onwards and reduced in length to allow it to be worn easily on the waistband:

The thigh strap was cut off and the long vertical strap shortened and folded back on itself before being sewn to create a belt loop:

Note the remaining taper from when this was a full length strap, and the pencil markings used to correctly attach the buckle in its original configuration. The other features of the holster are unchanged, so we have six woven loops for spare cartridges, the single strap to secure the revolver and the channel for the cleaning rod:

The base of the holster has a single brass grommet to allow any water to flow out:

The modified design was clearly popular as they began to be manufactured in this form from new from 1943 onwards- this example was originally made in 1942 before being modified- and the design continued in production into the post-war period as well.

If you want to find out more about the 1937 pattern webbing set, its production and use, check out my book here.