A grenade has been defined as a slow moving, high trajectory missile containing high explosive and exploding by contact or time fuse. Grenades may be divided roughly into two classes--1, hand grenades, and 2, rifle grenades, and each of these classes may be subdivided as regards means of explosion, into 1, time fuse, or 2, percussion grenades. Among the time-fuse hand grenades may be mentioned the Mills No. 5, Stokes bomb, smoke bombs, fumite bombs, etc. The Mills is easily the most important and has come to be the standard adopted by the Allies. The percussion grenade is little used--the most important among those of this type is the so-called "mushroom," named from its shape. Chief among the rifle grenades may be mentioned the Mills No. 23, the Hale No. 3 and the Newton No. 24. Just as the Mills hand grenade has become the standard, so has the Mills rifle grenade attained that pre-eminence. A more detailed description of the various sorts of grenades cannot be attempted in this brief space; but one or two diagrams at the close of the chapter may serve to clarify the subject to some extent. Any course in grenade training should have a three-fold purpose: 1st. To give the individual a practical knowledge of the working of the grenades in use. 2nd. To teach him how to throw them. 3rd. To make him acquainted with the general principles of organization and the execution of a grenade attack, either as a separate operation or as a part of a general attack. The time spent on any such course of training is a matter to be settled in the light of local considerations; but for purposes of preliminary training of a great number of men a period of two weeks is usually sufficient, with time allotted according to some such plan as this: (1) 10 separate half-hour sessions of practice in throwing from various positions and at the various targets; (2) 2 hours of study and a like amount of time spent in a conference for the purpose of clearing up matters that are hazy. In this brief time (only 9 hours) the foundation may be laid for a more thorough training of the specialists later on. In any such course the use of dummy grenades should always precede the use of any live ones; and men should be taught caution above all other things. This is a point easily lost sight of when men are using only dummies; but it is well worth remembering, for obvious reasons.