Infantry of most 21st-century armies are still trained in formation manoeuvre and drill, as a way of instilling discipline and unit cohesion. Members of the US Army utilize the term "line company" (informally) in light infantry battalions to differentiate those companies (generally A–D) that perform the traditional infantry role from the support companies (generally F and HHC) charged with supporting the "line companies". The Marine Corps does the same for all its infantry units. In this vein, officers assigned to the rifle companies are referred to as "line officers" while billeted to positions such as Platoon Leaders and Commanding and Executive Officers.