In dealing with the subject of the care of machine, guns for aircraft mounting, it is assumed that the officers and men for whose use this handbook is intended are thoroughly familiar with the operation of these guns. Each man should have in his possession the handbooks issued by the Ordnance Department, which take up the subject of each gun in detail. These handbooks are given in the "List of reference books" and may be obtained from the Ordnance Department upon request. It will therefore be necessary to consider here only that phase of the subject of the care of the guns which applies particularly to aircraft. This will consist of a description of the special devices and attachments, with instructions concerning their use and care, and a list of precautions to be observed in connection with the care and adjustment of the guns.

Machine guns for aircraft are divided into two classes according to the type of mount for which they are adapted. . The guns intended for installation on a fixed mount are Marlin, Browning, and Vickers.

The guns intended for installation on a flexible mount are Lewis.

The gun installed on a fixed mount is rigidly attached to the aircraft and synchronized with the engine, so as to make it possible to shoot between the blades of the propeller. The gun installed on a flexible mount does not shoot etween the blades of the propeller and may be aimed independently of the machine. The mounts and synchronizing devices will be dealt with in a later section.