Towed 4.2" Mortar

[horsa]

Looking for reference information to the photo linked above. I've had a photocopy of it for about six years and it is from a copy a friend has had longer than that. Trying to determine what book it came from and/or anything else specific to the towed British 4.2" mortar with ammunition trailer as shown.

Showing the entire page since its all I have to go from and thought someone might recognize one or both shots on it. My friend that originated it has no idea where he got it but it would appear to be book format.

Thanks in advance.

David