nmbm[23] - In the army now ...

Sidecar outfits were a popular means of transporting what were relatively heavy machine guns and their ammunition in both world wars.
The far 'bike is typical of the WW1 solution for a Vickers or Lewis gun - with their water jacket & ammo - plus the sidecar has some limited protection for the gunner.
[note that the headlamp is not blacked out on either 'bike]
The nearer bike is a Norton, also with some protection for the gunner [although that looks more like a "bren" to me] {& that's a civilian regno, the army no is on the tank}