1922 Encyclopædia Britannica/Helmet
HELMET (see 13.247).—The World War again demonstrated the truth of the old saying that “in war it is the unexpected that happens.” In view of the developments which had taken place in the science of gunnery, and the destructive effects of modern gun and rifle fire, it would hardly have been anticipated that the world would again witness the spectacle of soldiers in helmets throwing hand grenades and bombs at an enemy only a few yards distant—in fact, a return of the grenadiers in helmets. Against modern rifle-fire, helmets are of no use; and except for ornamental purposes they had long been abandoned. But the World War brought them again into use.
It was not until the war was well advanced, and the armies on the western front had been engaged in trench warfare for some considerable time, that it was realized that a great number of head wounds caused by shrapnel bullets, fragments of shell, etc., travelling at relatively low velocities, might have been prevented by very slight protection. Even then an immense amount of research and experimental work had to be carried out before an efficient helmet was produced, and an immense amount of prejudice had to be overcome before the soldier realized its value and could be induced to wear it. Helmets were first introduced into the French army, and they eventually formed an essential part of the equipment of every soldier.
The problem to be solved in the manufacture of a helmet is very different to that of the ordinary bullet-proof plate which is designed to stop direct rifle-fire. The governing factor is weight, and as it is impossible to attempt to stop direct rifle-fire owing to the excessive weight of metal which this would necessitate, efforts must be confined to securing defence against shrapnel bullets and fragments travelling at low velocities. A hard steel is out of the question, as it would break up under impact. On the other hand a soft steel would be too easily perforated. The properties which the metal must possess are those of extreme toughness and ductility, so that the resistance offered to the impact may be gradual and distributed over as large an area as possible. The effect can perhaps be best described by comparing it with the action of a loosely hung net in stopping a cricket ball or a golf ball. The one material which possesses these requirements to a high degree is manganese steel. This steel can be rolled into thin sheets from which the helmets are pressed, and in this form its ductility is remarkable. The thickness of the metal is only 20 B.W.G. or .036 of an inch, and this is required to withstand the impact of a shrapnel bullet (forty-one to the pound) travelling at a velocity of 750 ft. per second. Under actual test they resisted this attack at 900 ft. per second.
A comparison of the British helmet with the French and German is of interest. The French helmet weighed slightly less than the British—23¼ oz. as against 25½ oz.—but was only made of mild steel and could be easily perforated by shrapnel bullets at as low a velocity as 350 ft. per second. It must be remembered, however, that the French were the first to realize the value of helmets, and at once issued two million of them manufactured from the only material available to the army. Arrangements were subsequently made for these helmets to be replaced by manganese-steel helmets, but in the meantime the Armistice was signed and they were never delivered. The German helmet was made of nickel-chrome steel and weighed as much as 37 oz., or nearly 12 oz. more than the British. It was easily perforated by shrapnel at low velocities, and in addition suffered from the fatal defect of cracking and breaking under impact. The helmets supplied to the U.S. troops at the beginning of the war were exact copies of the British types. The model of 1917, of manganese steel, .036 in. to .040 in. thick, weighs, complete with lining and chin strap, 36 ounces. (E. F. L.)