For the film, see Second in Command. Second in Command is a 2006 Action film directed by Simon Fellows, starring Jean-Claude Van Damme.

A labeled image of a Parade Commander, Parade Second-in-command, and Squad Commander.

The Second-in-Command (2i/c or 2IC) is the deputy commander of any British Army or Royal Marines unit, from battalion or regiment downwards. The British Army is the land armed forces branch of the British Armed Forces. The Royal Marines ( RM) are the marine corps and amphibious Infantry of the United Kingdom and along with the Royal Navy A battalion is a Military unit of around 500-1500 men usually consisting of between two and seven companies and typically commanded by a Lieutenant Colonel A regiment is a Military unit, composed of a variable number of Battalions – commanded by a Colonel. He or she is thus the equivalent of an Executive Officer in the United States Army. While executive officer literally refers to a person responsible for the performance of duties involved in running an Organization, the exact meaning of the role is variable The United States Army is a military organization whose primary mission is to "provide necessary forces and capabilities. This terminology is also used in many other Commonwealth armies.

The Second-in-Command of a battalion or regiment is usually a Major. Major is a Military rank the use of which varies according to country The Second-in-Command of a company, squadron or artillery battery (in which he or she is called the Battery Captain) is usually a Captain (although infantry company Second-in-Command's were usually Lieutenants until after the Second World War), the Second-in-Command of a platoon or troop is the Platoon or Troop Sergeant, and the Second-in-Command of a section is usually a Lance Corporal. A company is a Military unit, typically consisting of 75-200 Soldiers Most companies are formed of three to five Platoons although the exact number may vary A squadron is a small unit or formation of Cavalry, armour, Aircraft (including Balloons) or Warships Army In Military organizations an artillery battery is a unit of Guns mortars or Rockets so grouped in order to facilitate better battlefield The Infantry is the oldest and most numerous of the Combat Arms in the Armed forces, and consists Lieutenant (abbreviated Lt or Lieut) is a Military, Naval, Paramilitary, Fire service, Emergency medical services World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including A platoon is a military unit typically composed of two to four sections or Squads and containing about 30 to 50 soldiers A troop is a Military unit, originally a small force of Cavalry, subordinate to a Squadron and headed by the troop leader Sergeant is a rank used in some form by most militaries police forces and other uniformed organizations around the world A section is a small Infantry unit first introduced in the British Army. Lance Corporal is a Military rank, used by many armed forces worldwide and also by some Police forces and other uniformed organizations

In the Royal Navy the second-in-command of a vessel is known as the First Lieutenant or Executive Officer. The Royal Navy of the United Kingdom is the oldest of the British armed services (and is therefore known as the Senior Service) First Lieutenant is a Military rank. The rank of Lieutenant has different meanings in different military formations (see Comparative military ranks

Other meanings/uses

Less formally, "second-in-command" is a term used, usually unofficially and sometimes jocularly, for any deputy. Its basic meaning is "someone who relieves a commander".