The EM-2 was the first prototype of an innovative weapon with the compact bullpup layout and an optical sight. It used one of the early intermediate cartridges, a highly efficient .280 British round, which was designed to replace the venerable .303 round and Lee-Enfield rifle variants which had served since before the turn of the 20th century. The British Army had originally planned to replace their .303 inch rimmed cartridge before World War I, but were forced to keep it due to time and financial constraints for another 30 years. With these constraints removed, they developed a new .280 inch (7 mm) intermediate-power round, and set about developing a new rifle to fire it.
Development of both round and rifle actually started while Britain was still occupied by German forces and this environment was reflected in the early postwar models of the EM-2 that showed considerable German influence. This resulted ina complex and highly-engineered weapon that performed extremely well when it worked at all but was expensive, difficult to manufacture and prone to failure. At this point, a Polish refugee, Captain Kazimierz Januszewski came to the rescue and redsigned the weapon with substantial input from the AK-47 rifle that was being introduced in Russia. The resulting weapon was the EM-3 that showed much-improved performance in a new series of trials. The EM-3 was adopted for service and briefy redesignated Rifle, 7mm No.10 before a new numbering system saw it being designated the L1. The EM-3 designation was retained for a civilian version that was intended for export, primarily to the United States.
Initial service experience with the new L1 was mixed. There was no doubt that the weapon performed well and gave the British Army a world-class assault rifle. However, it was almost impossible for left-handed shooters to use, the sight base was short, impeding accuracy and the weapon was equipped with a fixed 20-round magazine that was loaded by stripper clips. Perhaps worst of all from the point of view of the British drill sergeants, the short length of the weapon made much of the existing drill manual inappropriate.
These faults were quickly fixed with the definitive L1A1 model. This saw the fixed magazine replaced by a detachable 20-round box magazine and an optical sight issued for use with the weapon. This made the British Army the first to issue such sights as standard. The initial optical sight proved to be fragile but later versions proved to be robust and very effective. By 1960, the British Army was fully equipped with the new L1A1 rifle.