At the outbreak of the First World War, most of the machine guns employed by the major powers were large and heavy. Ideally suited to defense, few were actually light enough to be used in an offensive advance.
The weight of such small arms, and the fact that many were water-cooled to keep the barrel from overheating, made these impractical in an assault. However, military planners quickly considered ways to provide greater mobility along with sustained fire.
Germany: MG08/15 Machine Gun
The Germans saw the effectiveness of their MG08 machine gun and in 1915 developed a version for offensive use. The MG08/15 replaced the rear spade grips with a pistol grip and wooden buttstock. It also featured a short bipod rather than the heavy four-legged sled mount. However, it retained the bulky water jacket, which resulted in a weapon that weighed nearly 40 pounds and that was without water in the jacket or ammunition.