A bullpup firearm is one with its firing grip located in front of the breech of the weapon, instead of behind it. This creates a weapon with a shorter overall length for a given barrel length, and one that is often lighter, more compact, concealable and more maneuverable than a conventionally configured firearm. Where it is desirable for troops to be issued a more compact weapon, the use of a bullpup configuration allows for barrel length to be retained, thus preserving muzzle velocity, range and ballistic effectiveness.

The EM-2, also known as Rifle, No.9, Mk.1 or Janson rifle, was a British assault rifle. It was briefly adopted by British forces in 1951, but the decision was overturned very shortly thereafter by Winston Churchill's incoming government in an effort to secure NATO standardisation of small arms and ammunition. It was an innovative weapon with the compact bullpup layout, built-in carrying handle and an optical sight.