World War II to derive winter warfare factors pertaining to military tactics, materiel and personnel: Tactics – Defensive positions are highly advantageous because of the ability to maintain warmth and protection, compared to attacking in extreme cold. Mobility and logistical support are often restricted by snow, requiring plowing or compacting it to accommodate wide-tracked vehicles or sleds. Infantry movement in deep snow requires skis or snowshoes to avoid exhaustion. Sound carries well over crusted snow, diminishing the element of surprise. Explosives are useful for excavating foxholes and larger shelters in frozen ground. Attacking field kitchens and encampments deprives the enemy of food and shelter. Rapid removal of the wounded from the battlefield is essential to their survival in the cold. Materiel – Weapons and vehicles require special lubricants to operate at low temperatures. Mines are unreliable in winter, owing to deep snow that may cushion the fuse or form an ice bridge over the detonator. Personnel – Proper winter clothing is required to maintain body heat and to avoid such cold injuries as frostbite. Troop efficiency and survival requires either making use of available shelter or providing portable shelter. Land operations Operational factors encompass planning for the climate and weather in which military operations are required with snow, ice, mud and cold being the primary considerations. Military tactics, materiel, combat engineering and military medicine all require specialized adaptations to the conditions encountered in cold weather. The Soviet Army was an early adopter of a protocol for winter warfare. Cold and mountainous regions In its 2016 "Mountain Warfare and Cold Weather Operations" manual, the US Army defines cold regions as "where cold temperatures, unique terrain, and snowfall have a significant effect on military operations for one month or more each year." It describes regions that are either severely cold or moderately cold, each comprising approximately one quarter of the Earth's land mass. Severely cold – Where mean annual air temperatures stay below freezing, maximum snow depths exceed , and ice covers lakes and rivers for more than 180 days each year. Moderately cold – Where the mean temperatures during the coldest month are below freezing. The manual also delineates the principal mountain ranges of the world, which lie along broad belts which encircle the Pacific basin and then lead westward across Eurasia into North Africa. Secondarily, rugged chains of mountains lie along the Atlantic margins of the Americas and Europe. Weather