According to Wikipedia, early in World War II, during the fighting in North Africa, U.S. forces employed the slit trench — a very shallow excavation allowing one man to lie horizontally while shielding his body from nearby shell bursts and small arms fire — but after the Battle of Kasserine Pass, U.S. troops increasingly adopted the modern foxhole — a vertical, bottle-shaped hole that allowed a soldier to stand and fight with head and shoulders exposed.
Whether he is serving in the rocky wastes of Egypt or in the jungles of New Guinea, the American infantryman quickly discovers that the ground is his best friend in time of trouble. It is a lesson that no soldier ever learns too soon, for in the degree that it becomes his habit to seek protection even when halted for a few minutes, and to study the nature of cover and the elements of personal protection while he is in training, he increases his chance to survive in combat and to defeat the enemy.
The Basic Field Manual tells the story: You are most exposed to fire when you are standing, much less when you are prone, and best protected when you are below the surface of the ground. For example, under artillery shell fire, ten out of ten men would be hit by shell fragments if they were standing. Only six of the ten would be hit if all were prone. Only one would be hit if they were in shallow trenches or in foxholes.
Yet the swing back to intensive training in the nature and need of hasty field fortifications is a relatively new thing. During the first two years of the present war, the value of improvised works was greatly discounted, at first because of the emphasis on permanent fortifications, and subsequently because of the feeling that due to the influence of the high velocity weapons, the days of fixed positional warfare were over for good. From necessity, troops who were virtually without knowledge of how to dig and revet a trench of the 1914–18 variety soon learned how to scratch out air-raid trenches. Within the last year many occasions have arisen — in Libya, in Bataan, in Malaya and in Alaska — when a capacity to dig in quickly meant the difference between saving or losing a situation.
Very quickly the new technic of hasty fortification, as shaped by the need for protection against the tank and the airplane, has become standardized in line with the commonsense principle of achieving the maximum of protection in the minimum of time. Speed is the essence of today’s entrenching methods as it is of the modern offensive. The old type of trench — a much more elaborate affair — did not give adequate concealment from air and ground reconnaissance. Consequently, it is a conspicuous target for heavy concentrations of fire from aircraft and from ground weapons.
The new methods are designed to make all types of bombardment relatively ineffective by diffusing the target and giving greater individual protection to the soldier. Moreover, armored vehicles are not effective against infantry which they cannot see.
The special requirements of today’s warfare are therefore met when the soldiers are located in small one or two-man foxholes. To add to the enemy’s confusion, use may be made of decoy positions constructed in the general area of those which are to be occupied. Care must be taken to apply the same camouflage to the dummy positions as to the genuine ones.
Whenever our troops halt anywhere within range of Jap or Nazi bombers, they turn at once to give themselves and their weapons individual protection. If it’s a short halt, they use the natural protection of the ground — bumps, ditches, shell holes, ravines or depressions of any kind. But if it’s a longer halt — though less than six hours in an assembly area before an attack — then each man digs himself an individual prone trench. It can be done in a few minutes. That kind of a shelter gives a solider two advantages — a chance to rest and reasonable protection from bomb, mortar and shell fragments and small-arms fire. The prone trench, however, is not suitable protection against a tank attack.
If an outfit is to halt for more than five or six hours, it goes to work at once on standing-type one-man foxholes. These will protect the soldier against all bombs and shells, excepting direct hits, as well as small-arms fire. If the foxhole is dug deep enough to leave a clearance of two feet between the soldier and the surface of the ground, it is possible by crouching to obtain protection against the average enemy tank.
In digging this type of foxhole, the sod is put to one side. The rest of the dirt is then piled irregularly around the edges of the hole. When digging is completed, the sod is used to cover the rest of the dirt.
To quote the manual: “You must learn to study the terrain in order to appreciate the cover… that appears flat to the untrained eye.”
The wise foot soldier does not wait until he moves into the combat area before developing a practiced eye. He begins wherever he is doing duty, upon the ground over which he moves in his daily training.