The .303 British Bren light machine gun was originally developed as a replacement for the Lewis gun, which was prone to overheating on the battlefield. Just before WWII, the British engineered the Bren with a quick-change barrel system so they could stay in the fight when things got heated.
The Bren’s top-feeding magazine design also became one of its iconic features. Gravity-assited feeding also allowed soldiers to change magazines easily when shooting prone, but naturally the sight picture became obstructed. As a result, the weapon was often fired with a two-man team, and side-mounted sights became standard.
Check out the British Bren in action on this segment of Guns & Ammo TV.