Comment on 11. Month 11. Day 11. Hour by tuomaskoivurinne
The MG 08/15 is barely manportable. The Germans only developed an air cooled "light role" machinegun late in the war with the MG 08/18; which was superior in some ways to the Lewis gun, being belt rather than magazine (drum) fed. This made it better for laying down a base of fire to support an attack; but less mobile to support the maneuvre of the attack.
Indeed, but MG08/18 way too late to have good impact to the war. Just like MP18 "Maschinenpistole", which would have been an infantry close-quarters "super" weapon, if had more in numbers and earlier in time. I believe first MP18s appeared in actual battle around May -18 and still remained a rarity until the end of the war. Please read my reply to briantk2003 below 
Quite. If the MG 08/18 and MP18 been in effect sooner, perhaps with a good tube-magazine-fed shotgun for the Germans, the Stosstruppe would have had the capability to annihilate most opposition quite easily.