Second lieutenant (called lieutenant governor in some countries) is a junior commissioned officer military rank in many armed forces, comparable to NATO OF-1a rank.

The rank of second lieutenant existed in the military forces of the Australian colonies and Australian Army until 1986.

In the colonial forces, which closely followed the practices of the British military, the rank of second lieutenant began to replace ranks such as Ensign and Cornet from 1871.

New appointments to the rank of second lieutenant ceased in the Regular Army in 1986.^[1] Immediately prior to this change, the rank had been effectively reserved for new graduates from the Officer Cadet School, Portsea which closed in 1985. (Graduates of the Australian Defence Force Academy (ADFA) and the Royal Military College, Duntroon (RMC-D) are commissioned as lieutenants.).^[2][3] The rank of second lieutenant is only appointed to officers in special appointments such as training institutions, university regiments and while under probation during training. Trainees undertaking Special Service Officer (SSO) training are also appointed at higher rank (as second lieutenants) than General Service Officer (GSO) trainees who start off at the rank of officer cadet (ADFA/Australian Army Reserve officer trainees) or staff cadet (Royal Military College, Duntroon).^[4]

Ranks equivalent to second lieutenant are Acting Sub-Lieutenant in the Royal Australian Navy and Pilot Officer in the Royal Australian Air Force.

The Canadian Forces adopted the rank with insignia of a single gold ring around the service dress uniform cuff for both army and air personnel upon unification in 1968 until the late 2000s.^[5][6] For a time, naval personnel used this rank but reverted to the Royal Canadian Navy rank of acting sub-lieutenant, though the CF green uniform was retained until the mid-1980s. Currently, the Canadian Army insignia for second lieutenant is a pip and the Royal Canadian Air Force insignia for lieutenant is one thick braid. The equivalent rank for the Royal Canadian Navy is acting sub-lieutenant. Also known as an Ensign in the Foot Guards units (Canadian Grenadier Guards & Governor General's Foot Guards).

The insignia consists of a metal-colored bar in accordance with the color of the ceremonial uniform buttons and hat's symbol.

For example, for the infantry, gold being the metal of the ceremonial dress' buttons, the symbol on the képi being a golden grenade with two crossed rifles, therefore the *Sous-Lieutenant'*s insignia is a gold-colored bar.

For cavalry or forest rangers (light infantry mobilised from the Water and Forests Corp), ceremonial dress' buttons were silver, as was the hunting horn on the forest commissioned officer's képi, therefore the *Sous-Lieutenant'*s insignia is a silver-colored bar.

The insignia consists of a single silver star (or a star and a bar for reserve officers). Officers holding this rank should be addressed as "Kyrie Anthypolochage" (Κύριε Ανθυπολοχαγέ) by their subordinates, or "Anthypolochage + family name" by their superior officers.

In Indonesia, "second lieutenant" is known as letnan dua (letda) which is the most junior ranked officer in the Indonesian Military. Cadets who graduate from the Indonesian Military Academy achieve this rank as young officers. Senior non-commissioned officers promoted to becoming commissioned officers go to the officer's candidate school (Sekolah Calon Perwira) in Bandung to achieve the second lieutenant rank. The lieutenant rank has two levels, which are second lieutenant (Letda) and First lieutenant (Lettu). Lieutenants in Indonesia usually command a platoon level of troops and are referred to as "danton" abbreviated from komandan pleton (platoon commander) in Indonesian.

Since 1951 in the Israel Defense Forces (סגן-משנה (סג"מ segen mishne (sagam) has been equivalent to a second lieutenant (NATO OF-1). From 1948 – 1951 the corresponding rank was that of a (סגן) segen, which since 1951 has been equivalent to lieutenant. Segen mishne means "junior lieutenant" and segen literally translates as "assistant". Typically it is the rank of a platoon commander. Note that the IDF uses this rank across all three of its services.

Like many other Commonwealth countries, the rank structures of the New Zealand Defence Force usually follow British traditions. Hence the New Zealand Army maintains a rank of second lieutenant and the Royal New Zealand Air Force has its exact equivalent, Pilot Officer.

However, the Royal New Zealand Navy breaks with British tradition and uses the name ensign for its most junior commissioned officer rank (rather than the usual equivalents, such as acting sub-lieutenant or second lieutenant).

The equivalent rank in Norway (O-1) is "fenrik". This is the first rank, where they are commanding officer. Fenriks are usually former experienced sergeants but to become a fenrik one has to go through officer's training and education. Fenriks fill roles as second in command within a platoon. Fenriks are in some cases executive officers. Most fenriks have finished the War Academy as well, and are fully trained officers. To qualify for the Military Academy, Fenriks are required to do minimum 6 months service in international missions, before or after graduation.

The Pakistan Army follows the British pattern of ranks. A second lieutenant is represented by one metal pip on each shoulder in case of "khaki uniform" and one four quadric printed star on the chest in case of camouflage combat dress. However a second lieutenant in the Pakistan Army is usually promoted to lieutenant 6 months after commissioning.

In Singapore, the rank of second lieutenant (2LT) is given to officer cadets who have completed their Officer Cadet Course, and is the lowest commissioned rank in the Singapore Armed Forces, below the rank of lieutenant and above the rank of chief warrant officer. The rank insignia of 2LT is a bar.^[7]

The rank of second lieutenant (2Lt; colloquially known as a one-pip) was introduced throughout the British Army in 1877 to replace the short-lived rank of sub-lieutenant, although it had long been used in the Royal Artillery, Royal Engineers, Fusilier and Rifle regiments. At first the rank bore no distinct insignia. In 1902, a single Bath star (now commonly referred to as a pip) was introduced; the ranks of lieutenant and captain had their number of stars increased by one to (respectively) two and three. The rank is also used by the Royal Marines.

New British Army officers are normally commissioned as second lieutenants at the end of their commissioning course at RMA Sandhurst, and continue with specific training with their units, often with mentoring from senior NCOs. Progression to lieutenant rank usually occurs after about a year. In the British armed forces, second lieutenant is a rank which is not used as a form of address. Instead a second lieutenant named, for example, Smith is addressed and referred to as Mr Smith, with the exception that the alternative titles ensign and cornet are still used verbally in the Foot Guards and the Blues and Royals^[8] respectively. As these form six of the seven regiments that comprise the Household Division, the Life Guards are therefore the only Household regiment to which the exception does not apply.

In the Royal Air Force, the comparable rank is pilot officer. The Royal Navy has no exact equivalent rank, and a second lieutenant is senior to a Royal Navy midshipman but junior to a sub-lieutenant.

In the United States, second lieutenant is the normal entry-level rank for most commissioned officers in the Army, Air Force and Marine Corps and is equivalent to the rank of ensign in the Navy and Coast Guard.

In the Army and Marine Corps, a second lieutenant typically leads a platoon-size element (16 to 44 soldiers or Marines). In the army, until December 1917, the rank bore no insignia other than a brown sleeve braid on blouses and an officer's cap device and hat cord. In December 1917, a gold-colored bar similar to the silver-colored bar of a first lieutenant was introduced. In US military slang, the rank is sometimes called "butterbar" in reference to the insignia.^[9]

In the Air Force, depending upon the career field, a second lieutenant (2nd Lt) may supervise flights (of varying sizes) as a flight leader or deputy flight leader, or may work in a variety of administrative positions at the squadron, group, or wing level. A significant number of Air Force second lieutenants are full-time flight students in training for eventual designation as USAF pilots, combat systems officers or air battle managers.

The following are a selection of second lieutenant rank insignia, attempting to illustrate the range of variation (and similarity) between the insignia. Note that although many air forces use the rank of second lieutenant, in most Commonwealth air forces the equivalent rank of pilot officer is used. Very few navies use the rank "second lieutenant".

Note: U.S. Marine Corps (USMC) second lieutenant insignia bars have rounded off edges (no bevels), identical to the U.S. Navy ensign rank.^[10]