Second-in-command (2i/c or 2IC) is a title denoting that the holder of the title is the second-highest authority within a certain organisation. In the British Army or Royal Marines, the second-in-command is the deputy commander of a unit, from battalion or regiment downwards. This terminology is also used in many other Commonwealth armies and other nations. The equivalent appointment in the United States Army is the executive officer. In the Royal Navy and Commonwealth navies, the second-in-command of a vessel, regardless of rank, is known as the first lieutenant or executive officer.
