I was curious to see whether early war Commandos were organized differently and so I looked them up. Here is the standard Commando OOB that was used until the reorganization/re-equipping of August/September 1943.
There was no dedicated Heavy Weapons Troop originally – but 3in. mortars and Vickers MGs were used on an ad hoc mission-by-mission basis when they were considered appropriate. The permanent Heavy Weapons Troop was introduced as the Commandos began to be used more as assault troops rather than as hit-and-run raiders.