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.
The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkh ...
The Corps of Royal Marines (RM), also known as the Royal Marines Commandos, are the UK's special operations capable commando force, amphibious light infantry and also one of the five fighting arms of the Royal Navy. The Corps of Royal Marin ...
, the second-in-command is the deputy commander of a unit, from
A battalion is a military unit, typically consisting of 300 to 1,200 soldiers commanded by a lieutenant colonel, and subdivided into a number of companies (usually each commanded by a major or a captain). In some countries, battalions are ...
A regiment is a military unit. Its role and size varies markedly, depending on the country, service and/or a specialisation.
In Medieval Europe, the term "regiment" denoted any large body of front-line soldiers, recruited or conscripted ...
downwards. This terminology is also used in many other Commonwealth
armies and other nations. The equivalent appointment in the
United States Army
The United States Army (USA) is the land warfare, land military branch, service branch of the United States Armed Forces. It is one of the eight Uniformed services of the United States, U.S. uniformed services, and is designated as the Army o ...
An executive officer is a person who is principally responsible for leading all or part of an organization, although the exact nature of the role varies depending on the organization. In many militaries and police forces, an executive officer, o ...
The second-in-command of a battalion or regiment is usually a
Major (commandant in certain jurisdictions) is a military rank of commissioned officer status, with corresponding ranks existing in many military forces throughout the world. When used unhyphenated and in conjunction with no other indicators ...
. The second-in-command of a
A company, abbreviated as co., is a legal entity representing an association of people, whether natural, legal or a mixture of both, with a specific objective. Company members share a common purpose and unite to achieve specific, declared ...
In military organizations, an artillery battery is a unit or multiple systems of artillery, mortar systems, rocket artillery, multiple rocket launchers, surface-to-surface missiles, ballistic missiles, cruise missiles, etc., so grouped to fac ...
(in which they are called the battery captain) is usually a
Captain is a title, an appellative for the commanding officer of a military unit; the supreme leader of a navy ship, merchant ship, aeroplane, spacecraft, or other vessel; or the commander of a port, fire or police department, election precinct, e ...
Infantry is a military specialization which engages in ground combat on foot. Infantry generally consists of light infantry, mountain infantry, motorized infantry & mechanized infantry, airborne infantry, air assault infantry, and mar ...
company second-in-commands were usually
A lieutenant ( , ; abbreviated Lt., Lt, LT, Lieut and similar) is a commissioned officer rank in the armed forces of many nations.
The meaning of lieutenant differs in different militaries (see comparative military ranks), but it is often s ...
s until after the
Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
), the second-in-command of a
A platoon is a military unit typically composed of two or more squads, sections, or patrols. Platoon organization varies depending on the country and the branch, but a platoon can be composed of 50 people, although specific platoons may range ...
is the platoon or troop
Sergeant ( abbreviated to Sgt. and capitalized when used as a named person's title) is a rank in many uniformed organizations, principally military and policing forces. The alternative spelling, ''serjeant'', is used in The Rifles and other ...
, and the second-in-command of a section
is usually a
Lance corporal is a military rank, used by many armed forces worldwide, and also by some police forces and other uniformed organisations. It is below the rank of corporal, and is typically the lowest non-commissioned officer (NCO), usually equi ...
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by Kingdom of England, English and Kingdom of Scotland, Scottish kings from the early medieval period, the first major maritime engagements were foug ...
and Commonwealth navies, the second-in-command of a vessel, regardless of rank, is known as the
First lieutenant is a commissioned officer military rank in many armed forces; in some forces, it is an appointment.
The rank of lieutenant has different meanings in different military formations, but in most forces it is sub-divided into a se ...
or executive officer.
In common usage, the term refers to a deputy
. Its basic meaning is "someone who relieves a commander".