Sub - lieutenant Sub - lieutenant is a military rank . It is normally a junior officer rank . In many navies , a sub - lieutenant is a naval commissioned or subordinate officer , ranking below a lieutenant . In the Royal Navy ( RN ) the rank of sub - lieutenant is equivalent to the rank of lieutenant in the British Army and of flying officer in the Royal Air Force ( RAF ) . An RN sub - lieutenant ranks above an Army second lieutenant or an RAF pilot officer . In some armies , sub - lieutenant is the lowest officer rank . However in Brazil it is the highest non - commissioned rank , and in Spain it is the second highest non - commissioned rank . The NATO rank code is OF - 1 ( senior ) . History of naval rank . In the British Royal Navy , a passed midshipman awaiting promotion often elected to become a master ' s mate , normally an experienced petty officer who assisted the sailing master . Though formally the rating did not lead to promotion to lieutenant , master ' s mates were paid more than any other rating and were the only ratings allowed to command any sort of vessel . A midshipman who became a master ' s mate got an increase in pay from £ 1 13 s 6 d to £3 16s per month , but initially reduced his chances at a commission . Over time , however , service as a master ' s mate became a normal part of the path to a commission . The situation caused some confusion during the last part of the 18th century , when two parallel roles — master ' s mates trying to become masters , and former midshipmen working toward a commission — held the same title and responsibilities aboard ship . By the first years of the 19th century , the prefix " master ' s " was dropped for passed midshipmen , to distinguish them from master ' s mates in the navigator ' s branch . In 1824 two further grades were also introduced , consisting of master ' s assistants and second - class volunteers . These corresponded to midshipmen and first - class volunteers respectively in the executive line . From this point , passed midshipmen had the rating master ' s mate , abbreviated as mate , and prospective masters had the rating master ' s assistant . These changes helped eliminate the confusion caused by the mingling of midshipmen in the navigator ' s branch . In 1838 a Royal Commission , presided over by the Duke of Wellington , recommended the institution of the rank of mate as an official step between midshipman and lieutenant . In 1861 mate was abolished in favour of sub - lieutenant . Acting sub - lieutenant . In 1955 , the Royal Navy created the rank of acting sub - lieutenant . Unlike their substantive counterparts , acting sub - lieutenants are subordinate officer s , as they hold their ranks by order and not by commission . Upon passing Fleet Board , acting sub - lieutenants were confirmed as sub - lieutenants and issued commissions backdated to the date when they were appointed acting sub - lieutenants . The rank of acting sub - lieutenants was abolished in the Royal Navy around 1993 , and now exists only in the Royal Naval Reserve . Before its abolition , the rank of acting sub - lieutenant in the Royal Navy corresponded with , but was junior to , the ranks of lieutenant ( Army ) and flying officer ( RAF ) . This can be seen in print versions of STANAG 2116 edition 5 ( 1992 ) . In many Commonwealth navies ( e . g . Canada and Australia ) however , the rank of acting sub - lieutenants still exists as a commissioned rank equivalent to Second lieutenant , while the rank of sub - lieutenant is equivalent to that of an army lieutenant . As the term " acting " is a designation , both acting and substantive ranks should be orally addressed as " sub - lieutenant ; " the full designation including " acting " should be used in written documents , however . Indeed , when someone is addressed as " Acting sub - lieutenant " it can be seen as a way of patronising an individual in a derogatory manner due to the emphasis of their " acting " rank . The Royal New Zealand Navy follows the US precedent in titling its lowest commissioned officer ensign . In the Royal Thai Army , Army Reserve Force Students who complete grade 5 and their B . D . are promoted to the rank of acting second lieutenant ( ว่าที่ ร้อยตรี ) . Modern practice . In the modern Royal Navy , those joining as graduates start as sub - lieutenants with non - graduates joining as midshipmen . Sub - lieutenants are confirmed in their rank and receive their commission parchments upon passing out of Britannia Royal Naval College . The same is true in the Royal Canadian Navy , with all undergoing basic officer training as Naval Cadet s , but upon graduation those who joined with a bachelor ' s degree receive an immediate promotion to Acting sub - lieutenant while those that do not retain their rank as Naval Cadet until such time as they finish more career - related training . Rank insignia : armies . In France , a sub - lieutenant ( " sous - lieutenant " ) is the junior commissioned officer in the army or the air force . He wears a band in the colour of his corps ( e . g . gold for infantry , silver for armoured cavalry , etc . ) . During the 18th century a rank of " sous - lieutenant de vaisseau " existed in the French Navy . It was the equivalent of the master ' s mate rank of the Royal Navy . It is now replaced by the rank of " first ensign " ( " enseigne de vaisseau de première classe " ) . In Argentina , a sub - lieutenant wears a single silver sun on each shoulder . In Brazil , a sub - lieutenant , the most senior non - commissioned rank , wears a golden lozenge . In Mexico , the sub - lieutenant is the junior officer in the rank scale , wearing a single gold bar . In Thailand , a sub - lieutenant and acting sub - lieutenant wears a single star on each shoulder . Rank insignia : naval . In the Royal Navy , the Royal Australian Navy and the Royal New Zealand Navy , the insignia of both sub - lieutenants and acting sub - lieutenants consists of one medium gold braid stripe with an executive curl . The size of this stripe should not be confused with the narrow stripe , colloquially referred to as " spaghetti strap , " used on the Royal New Zealand Navy rank of ensign and the Royal Canadian Navy ' s naval cadets . The Royal Air Force also followed this example of braiding when developing their rank system ( see flying officer ) . The insignia of sub - lieutenants in most commonwealth countries are identical to the United States Navy and United States Coast Guard grade of ensign ( although US ranks do not use the executive curl ) , even though its equivalent grade in the USN is actually lieutenant junior grade . In the Royal Canadian Navy , acting sub - lieutenants display one medium stripe . A sub - lieutenant adds a narrow stripe " below " the medium stripe to maintain the executive curl on the top . The equivalent army and air force second lieutenant rank has the narrow stripe above the medium stripe , since these elements do not need to maintain spacing on top due to the lack of an executive curl ; the RCN followed this pattern before the addition of the curl in 2011 . British Army . The British Army briefly had a rank of sub - lieutenant in the late 19th century , replacing the ranks of ensign in the infantry and cornet in the cavalry . After a few years , it was replaced in turn by the rank of second lieutenant .