[Godwin Hampton]

Darrin, the 1951 Infantry Training pamphlet for the 3" Mortar shows a barrel with a removable breech piece, describing it as the Mk 5 barrel. The square baseplate with large holes and a chain handle at the rear of the top plate is called the No. 6 baseplate, and finally the bipod having stamped plates ( rather than forged ) joining the 2 legs to the elevating screw tube is described as the Mk 5 bipod.

Now these different versions of these 3 items could probably all be used together interchangably! So you could have a mortar having a Mk 3 barrel, a No 4 baseplate and a Mk 1 bipod!

The Small Arms Training pamphlets for 1939 and 1943 show the one-piece tube, the tapered corner baseplate and the bipod with forged horizontals joining the legs, without giving any marks or numbers.

The 1937 Handbook ( reprinted by The Naval and Military Press and very informative! ) probably issued when the mortar was accepted for service starts with the Mk 1 barrel, but gives no marks or numbers for the baseplate and bipod shown.

There were, thankfully, only 2 marks of sight which have a different mounting system so this also entails differences in the bipod sight supporting bracket.

So to simplify I divide the 3 inch ( actually 81mm ) mortar versions broadly into two types, the early with the one-piece tube, tapered baseplate and forged bipod and the later type with removable breech piece, square baseplate and stamped bipod.