130,694. Ellis, R. E., (Cook, C. J.) March 15, 1918. Machine guns; ordnance design; sights and methods of sighting; muzzle-loading. - Relates to " non-recoil " guns discharging projectiles at both ends of a barrel, and consists mainly in mounting such a gun outside the fuselage of an aeroplane in a direction parallel to the axis of the aeroplane. In the form shown, the gun 5, Fig. 1. is mounted on horizontal trunnions in brackets 7 depending from the aeroplane 1, and is connected by a link 8 to a trap door 9, which when opened tilts the gun to the position shown in dotted lines for convenience in loading. The charge comprises a projectile 11, Fig. 4, in front, a propellent explosive 12 in the middle, and a reaction mass 13 in the rear. The barrel is rifled and a spring plunger 20<1> or a spring pawl is provided to hold the charge in place until the gun is fired. The firing is done electrically through a plug 20, and is under control of a hand switch 23, Fig. 2, in series with a switch 26 on the propeller shaft 2<1>, in order to permit firing only when a propeller blade is not in front of the gun. The barrel a may be mounted between a pain of springs f, Fig. 6, within a sleeve b trunnioned to the brackets c. The abutment rings e of these springs are secured to the barrel a by shear wires, so that the springs take up small recoil movements, but an excessive recoil shears the wires and blows the barrel away without injuring the aeroplane. A machine gun 3, Fig. 1, fixed to the aeroplane in the same direction as the main gun 5, is used to discharge smoke or " tracer " bullets to indicate when the aim is correct, the aim being taken by manoeuvring the aeroplane.