German Methods of Crossing Ice, WWII Tactical and Technical Trends, No. 17, January 28, 1943 (Lone Sentry)

What follows is believed to be the official views of the German Army on the possibilities and limitations of ice in so far as it affects the passage of military traffic over water obstacles. However, while the views expressed are presumed to embody the lessons learned during the Russo-Finnish war of 1939-40, they do not embody the experience gained by the Germans during the Russian campaigns.

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In general, freezing conditions lessen the value of water as an obstacle and make the terrain more passable; this will tend to weaken the defense and strengthen the attack. On the other hand, ice floes and thin ice considerably increase the difficulty of crossings and necessitate special measures.

a. Roads Across Ice

The following are the loads which can be supported by sheets of solid ice of various thicknesses, lying on water:

Thickness		Load
1 1/2 in . . . . . . . . .		Single infantrymen
2 in . . . . . . . . . . .		Infantry in open order
4 in . . . . . . . . . . .		Single horses
6 in . . . . . . . . . . .		Infantry and horsed cavalry in column of march, with light motor transport
8 in . . . . . . . . . . .		Light artillery up to 2 1/2 tons, horse-drawn, and 4-ton wheeled vehicles, maximum axle load 2.7 tons, minimum interval 65 feet
1 ft . . . . . . . . . . .		10-ton wheeled vehicles, maximum axle load 7 tons, minimum interval 65 feet
1 ft 2 in . . . . . . . .		20-ton wheeled vehicles, minimum interval 100 feet

Experiments have shown that a sheet of ice 10 inches thick will carry tracked vehicles up to 16 tons at an interval of 165 feet, moving at a speed of not more than 2 1/2 mph, provided that track slip is avoided.

Ice will carry heavier loads over still water than over streams and rivers. The thickness of the ice may vary over the same stretch of water; if, for instance, warm springs are present the ice will tend to be thinner, or if the river bed is locally swampy it will tend to be thicker or even frozen solid through to the river bed. A layer of snow on the ice diminishes its strength, since the warmer water from the bottom does not cool on rising as readily as in the absence of snow, which tends to insulate the ice from the cold atmosphere. Warm weather (thaw) diminishes the carrying capacity of ice very rapidly, even when the thickness of the ice remains the same since the ice becomes somewhat porous. The thickness of ice should be determined by boring; at the same time it should be ascertained whether the ice is lying on water. In doubtful cases loading tests should be carried out. Holes and open patches (found mostly near the banks) should be treated with special care. Changes in water level, particularly associated with dams, must be carefully observed.

To prepare it for traffic, ice should be covered with gravel or sand. On both sides of the roadway over the ice a strip at least 16 feet wide should be kept free of snow, to permit observation of any cracks in the ice. Single cracks running transversely across the roadway do not appreciably diminish its carrying capacity, and can be closed in cold weather by pouring water on them. Heavy cracks running parallel to the track indicate that the carrying capacity of the ice is becoming exhausted.

In sufficiently cold weather, ice can be strengthened or reinforced by the addition of further ice layers. This can be done by the following methods:

(1) Laying and watering of sawn-out blocks of ice;

(2) Addition of water, using low snow dams, the water being allowed to freeze;

(3) Addition of straw, twigs, or reeds which are watered and allowed to freeze.

Strengthening of ice in the above manner can only be carried out if the ice is at least 1 inch thick. The carrying capacity of reinforced ice increases approximately according to the figures already given, but the capacity of the additional "artificial" layer should, in actual practice, be calculated as only half that of natural ice. In strengthening ice the width of the strengthened belt should be at least 2 1/2 times that of the roadway itself. After strengthening, small holes should be drilled in the ice in the neighborhood of the roadway; these will allow the water to seep through and improve the equilibrium of the ice-sheet. The roadway must be carefully marked off, and if in constant use, should be provided with a light surfacing.

Track for the passage of vehicles may be constructed of chess or other planking. Vehicles will normally run at very low speeds on two treadways. Joints of these treadways must be staggered to prevent simultaneous impact on both joints. The load may be spread by timbers placed under the treadway. If boards are placed as cross ties, they should be close enough together to insure that the heaviest loads do not bend the treadway sufficiently to strike the ice.

If ice is artificially strengthened, test loading must be carried out in each instance. The carrying capacity of ice may be diminished by excessively heavy track reinforcement.

For assault infantry crossings, the light assault bridge using planks instead of floats is suitable.

b. Use of Boats in the Presence of Ice

Assault boats, strengthened by thin metal sheeting along the water line, can be used as ice breakers, to cross water covered with ice up to an inch in thickness.

It is possible to negotiate streams filled with ice floes if the current is not too rapid and the floes are of sufficient size and thickness. Pontons must be protected by round timbers or planks secured to the sides with ropes. Floes must be kept off by men standing in the bow and using short boathooks. Large pneumatic boats can be protected in the same way.

c. Ice Bridges

With weather continuously freezing, ice bridges may be constructed to cross short stretches of open water or thin ice. A large block of ice, at least thirteen feet wide, as thick as practicable and several feet longer than the span of water or thin ice, is cut and moved to bridge the gap. This ice bridge may be strengthened according to the methods previously described.

In slowly moving water, it may be convenient to cut the block of ice adjacent to the bridge site and parallel to the bank (see sketch below). After removing the other ice on a ninety-degree arc, it is possible to pivot the block of ice about point A (see sketch) and use the current to swing it into place. Notches cut in the ice on the two sides of the bridge site will hold the block in place.

[German Ice Bridge]

d. Bridging in the Presence of Ice

In general, ice bridges should be replaced as soon as possible by regular bridges. Fixed supports are preferable to floating supports for this purpose. Long spans diminish the danger to the bridge on the breaking up of the ice. Piles should be shod with metal, and some form of ice breaker should be used. Floating supports must be capable of submerging when the bridge is loaded, and should be kept free from ice. Light boats and pontons will be crushed by thick ice, even in still water. For streams where the flow of ice is heavy and those in which the danger of break-up is great, bridges with floating supports cannot be used.

Construction of bridges in the presence of ice floes is difficult, and unforeseen incidents are of such frequent occurrence that definite figures for the time required cannot be laid down. Improvised bridges on floating supports can only be erected when floes are small and the density not too great; under these conditions the floes must be continually pushed away from the supports and allowed to pass under the finished bridge. With larger floes a bridge can only be built if the ice can be broken up at a sufficient distance upstream.

Anchor cables are apt to wear through after a short time; they should accordingly be preserved by being enclosed in three-sided wooden casings, about 10 feet in length, which keep the lines from direct contact with drifting ice. Wire ropes are especially suitable for use as anchor cables under these conditions. Rafts used for pile-driving must be protected from drift-ice by metal boats or floats anchored upstream.

When working on ice, it may be necessary to rope pairs or groups of men together for safety.

A party on guard upstream should be amply provided with explosives and fuzes for the destruction of ice.