In the United States Army and Marine Corps, for example, there are XO billets in each company, battalion, and brigade, though not at higher levels of command. The XO billet is not a command; rather it is considered staff. The XO is typically responsible for the management of day-to-day activities, such as maintenance and logistics, freeing the unit commander to concentrate on tactical planning and execution. The XO also takes charge in the absence of the CO. While the experience gained as an XO is highly beneficial for an officer's professional development, never serving in the position will not preclude an officer from commanding later. In the United States Navy and Coast Guard, XOs are normally assigned to all ships and shore units, and have a similar role to their counterparts in the Army and Marine Corps. On board Coast Guard cutters that are commanded by either a junior officer or a senior enlisted member, Executive Petty Officers (XPOs) are usually assigned to serve as second-in-command.