The reference to The Somme - Crucible of the British Army on the subject of artillerymen's underwear made me get the book out for the first time in years, and, to my surprise, there's a picture of German weapons captured on July 1st: MG08, Russian Maxim, LMW, and . . . a Madsen.
It's described as Muskete - Danish M1902 Madsen automatic rifle.The caption says, "The Madsen was used by Musketen Battalions, off which 3 were formed in 1915; their place was behind the first positions to cover any breach which might be made." So not cavalry, then?
Interesting - a cavalry weapon used by infantry I suspect these Madsens were from the consignment originally intended for Russia that the germans managed to extract from the Danes bu deception (see amuch earlier thread on this forum).
It looks as if Britain was correct in not acquiring Madsens (as had once been a posibility) and going for the Lewis instead. The Madsen appears to have had the general characteristics of a heavy sub machine gun (including limited magazine capacity) rather than a light machine gun.