First lieutenant

First lieutenant is a commissioned officer military rank in many armed forces and, in some forces, an appointment.

The rank of lieutenant has different meanings in different military formations (see comparative military ranks), but the majority of cases it is common for it to be sub-divided into a senior (first lieutenant) and junior (second lieutenant) rank. In navies it may relate to a particular post rather than a rank.

United Kingdom

British Army

In the British Army and Royal Marines, the rank above second lieutenant is simply lieutenant (pronounced lef-tenant), with no ordinal attached.

Before 1871, when the whole British Army switched to using the current rank of "lieutenant", the Royal Artillery, Royal Engineers and fusilier regiments used "first lieutenant" and "second lieutenant".

Royal Navy

The first lieutenant (often abbreviated "1st Lt") in a Royal Navy ship is a post or appointment, rather than a rank.

Historically the lieutenants in a ship were ranked in accordance with seniority, with the most senior being termed the first lieutenant and acting as the second-in-command, unless the ship was complemented with a commander. Although lieutenants are no longer ranked by seniority, the post of "first lieutenant" remains. In minor war vessels, destroyers and frigates the first lieutenant is second in command, executive officer (XO) and head of the executive branch; in larger ships where a commander of the warfare specialisation is appointed as the executive officer, a first lieutenant is appointed as his deputy. The post of first lieutenant in a shore establishment carries a similar responsibility to the first lieutenant of a capital ship. Colloquial terms in the Royal Navy for the first lieutenant include "number one", "the jimmy" (or "jimmy the one") and "James the First" (a back-formation referring to James I of England).