The Lee-Enfield was the main battle rifle of the British Army from 1895 to 1957. The particular version represented in WW1:Source is the SMLE Mark III variant (Short Magazine).
The first fragmentation grenade, the Mills bomb was developed by the British Army and adopted in 1915.
The main light machine gun of the British Army during WW1.
The German Reich's standard rifle from 1898 to 1935. It is considered by many to be progenitor of all the modern bolt action rifles thanks to its ingenuous turned-down bolt action design and to the fact it was one of the first weapons to be fitted with smokeless powder ammunition. Because of its length and practical operational range of 550 yards (500 meters), the rifle proved to be sometimes tricky to use in a trench warfare environment.
The Model 24 was better balanced than its British counterpart, due to the extra leverage given to it by the long wooden handle which gave the soldiers a better grip and handling. However, due to the limitations of the source engine, the Model 24 has a smaller range and lower flight path than it would have in real life.
The MG 08/15 was a cut down version of the MG 08, an adaption of Hiram Maxim's 1884 design. It has highly accurate sights and is fairly easy to operate.