maintain trails by establishing a well concealed track with the first vehicle, followed by a vehicle traveling offset from the track of the first, to flatten the trail, and subsequent vehicles widening and flattening the trail. Marked trails avoid obliteration in snowstorms or drifting conditions. In mountainous terrain, tracked vehicles, including tanks, infantry fighting vehicles, and cavalry fighting vehicles, rarely accompany dismounted infantry in the assault. Instead, they assist forces by occupying positions where they can use their firepower to isolate enemy objectives. Dismounted movement The German Taschenbuch describes preparation and conduct of marches and advocates maintaining slow, steady progress with brief stops to avoid exposure to the wind, and the provision of warm beverages by support vehicles along the way. Soviet Army doctrine emphasized the use ski troops for dismounted operations over snow. US Army guidance explains that troops moving in a wedge-like "column" formation travel more slowly, with no one breaking the trail in undisturbed snow, than the in-line file formation. Therefore, column formation is reserved for imminent enemy contact. As slope angle increases, the amount of travel time is likely to increase substantially. Water crossings The German Taschenbuch describes the assessment and reinforcement of ice crossings and also the opportunity to use them as tank traps by removing the ice and bridging the gap with a weak structure, disguised as reinforced ice. It offers the following guidance for crossing ice sheets: Soviet Army doctrine described the assessment and reinforcement of ice crossings and suggested the use of frozen lakes and rivers as expeditionary airfields, located close to the front to take advantage of short daylight hours in winter. According to the US Army, rivers found in cold regions may be major obstacles. Subarctic rivers usually have many braided channels and swift currents. During spring and early winter, rivers may become impassable due to freezing or thawing ice flows. Once firmly frozen, rivers may offer routes for both mounted and dismounted movement. Some swampy areas do not freeze solidly during the coldest periods of winter to support troop movements. Nonetheless, it is possible to construct "ice bridges" to thicken an iced-over waterway, using pumps or some other means of flooding the ice-covered area, when temperatures are below and the pre-existing natural ice is thicker than to support the construction activity. Snow camouflage Armies have made use of improvised and official snow camouflage uniforms and equipment since the First