For mechanical efficiency, opposite arms usually swing with each leg while marching. British and Commonwealth armed forces keep their arms straight and swing the hand as high as the shoulder while forward and in theory to the level of the belt when backward. US Marines swing the arm six inches to the front and three inches to the rear while US Army Soldiers swing the arm nine inches to the front and six inches to the rear. Some European armies bend the arm during the swing. Most foot drill instructors believe these differing practices are efficient i. e. maintain rhythm for long route marches. US troops usually march long distances at "route step" which does not require them to maintain a specific pace or length of step. Some South American and Eastern European countries march on parade with the stiff leg earlier famous as the "goose step" of German troops. German and Scandinavian military bands and units swing with only the right arm, 90 degrees straight out. Some troops (like the Royal Swedish Lifeguard) swing with their left arm. This is because they carry their rifle in their right arm.
Marching is part of basic training in the military in most countries. In most cases, marching uses a system of drill commands . Learning to march by obeying commands is considered a form of discipline .