The RH&DR armoured train packs a punch!
People who know about these things tell me the fat gun nearest the camera is a Lewis gun with the other one being a Bren. Not sure what the different or significance is but I'm sure you'd want to be at the trigger end rather then the other.
The Lewis is fitted to a pole so it can be swung around. The Bren is on a circular rail which I assume rotates. There is a fitting for a second weapon here, apparently a Boyes anti-tank rifle for when the Bosh are coming up the beach.
Fitting the guns is a superglue job. The Bren is moulded in to the soldier figure whereas the Lewis is a separate item. I've tested it with the figure and recon that the white metal support will bend to accommodate him.
(Information on guns picked up from the GnATTERbox forum)