A breakout may be attempted in conjunction with relief, and this may be essential especially if the invested force has already experienced failed breakout attempts (again, as in Winter Storm). As the situation on the Western Front during the First World War has been widely regarded as a single continent-long siege, rather than a series of distinct battles, it is possible to consider offensive action from the Allies as a type of breakout. In this sense the Allied armies may be considered encircled, albeit on a hitherto unheard of scale, with the German army to their east, the Alps and the Pyrenees to their south, and the sea to their west and north. Indeed, as the Dunkirk evacuation illustrated, despite having by far the largest navy in the world, the amphibious movements of these armies was nearly impossible logistically. Similarly, as seen at the Battle of Sarikamish, mountainous terrain remained a significant obstacle to military movement and could inflict numerous casualties. Breakout maneuvers, despite their own myriad risks, may become necessary by a number of disadvantages encircled forces suffer. The invested force suffers from the disadvantages resulting from occupying a confined space and also from those resulting from a lack of resupply. Therefore, the encircling force has a significant tactical advantage and also have the advantage of time. It may, in fact, choose to not engage their enemy at all and simply wait it out, leading to eventual exhaustion of ammunition if the invested force gives battle or to the eventual exhaustion of food and water otherwise. The US Army lists four conditions, one of which normally exists when a force attempts a breakout maneuver:   Of necessity, the broad concept is subject to interpretation. In "The Blitzkrieg Myth", John Mosier questions whether the concept as applied to tank and other warfare in World War II was more misleading to planning than it is helpful, on account of the numerous exceptional conditions faced in war and also whether evaluation based largely on how well breakout or breakthrough potential was realized is appropriate  An example is the battle of Hube's Pocket on the Eastern Front in World War II, where the German First Panzer Army was encircled by Soviet forces but broke out by attacking west and linking with the II SS Panzer Corps, which was breaking into the encirclement from outside.