The battles of Belleau Wood and the Argonne forest are the most famous battles of World War One in which the USA participated. These two battles are example of trench warfare, a very static way of fighting in which two armies dig a series of adjacent defensive lines, or trenches, and try to prevent the other army from advancing while simultaneously trying to advance themselves. Consequently an area known as “no man’s land” formed between the trenches and could at times be over half a mile across. There was little action in the no man's land during the day due to frequent suppressing fire from both sides. Under the cover of darkness however both sides would sneak over the top and search for any potential prisoners or to spy on the enemy's trench. Because crossing the no man’s land to attack was most dangerous, ways of protecting those crossing were sought after, the most effective of which were the heavily armored assault vehicles, or tanks. These tanks were virtually impervious to all but mortars and large bombs, making them ideal for crossing the no man’s land and clearing trenches.