The British had another scheme for locking the mechanism until after the grenade had traveled some distance through the air. Details of this grenade, which was of the type adopted to be fired from a rifle, are shown in Fig. 6. The striker _A_ is retained by a couple of bolts, _B_, which in turn are held in place by a sleeve, _C_. On the sleeve is a set of wind-vanes, _D_. As the grenade travels through the air, the wind-vanes cause the sleeve _C_ to revolve, screwing it down clear of the bolts _B_, which then drop out, permitting the pin _A_ to strike the detonator _E_ upon impact of the grenade with its target. [Illustration: FIG. 7. Front, side, and sectional views of a disk-shaped German grenade] [Illustration: FIG. 8. A curious German hand grenade shaped like a hair brush] The Germans had one peculiar type which was in the shape of a disk. In the disk were six tubes, four of which carried percussion caps so that the grenade was sure to explode no matter on which tube it fell. The disk was thrown with the edge up, and it would roll through the air. Another type of grenade was known as the hair-brush grenade because it had a rectangular body of tin about six inches long and two and three quarter inches wide and deep, which was nailed to a wooden handle. MINIATURE ARTILLERY Hand-artillery was very effective as far as it went, but it had its limitations. Grenades could not be made heavier than two pounds in weight if they were to be thrown by hand; in fact, most of them were much lighter than that. If they were fired from a rifle, the range was increased but the missile could not be made very much heavier. TNT is a very powerful explosive, but there is not room for much of it in a grenade the size of a large lemon. Trench fighting was a duel between forts, and while the hand-artillery provided a means of attacking the defenders of a fort, it made no impression on the walls of the fort. It corresponded to shrapnel fire on a miniature scale, and something corresponding to high-explosive fire on a small scale was necessary if the opposing fortifications were to be destroyed. To meet this problem, men cast their thoughts back to the primitive artillery of the Romans, who used to hurl great rocks at the enemy with catapults. And the trench fighters actually rigged up catapults with which they hurled heavy bombs at the enemy lines. All sorts of ingenious catapults were built, some modeled after the old Roman machines. In some of these stout timbers were used as springs, in others there were powerful coil springs. It was not necessary to cast the bombs far. For distant work the regular artillery could be used. What was needed was a short-distance gun for heavy missiles and that is what the catapult was. [Illustration: Press Illustrating Service A 3-inch Stokes mortar and two of its shells] [Illustration: Press Illustrating Service Dropping a shell into a 6-inch trench mortar]