Editing Pennant number (section)

==Royal Navy systems==
<ref>{{cite book |last1=Warlow |first1=Ben |last2=Bush |first2=Steve |title=Pendant Numbers of the Royal Navy |date=2021 |publisher=Seaforth |location=Barnsley |isbn=9781526793799}}</ref><ref>{{cite journal |last1=Dodson |first1=Aidan |title=The Development of the British Royal Navy's Pennant Numbers Between 1919 and 1940 |journal=Warship International |date=2024 |volume=61 |issue=2 |page=134–66}}</ref>

The Royal Navy first used pennants to distinguish its ships in 1661 with a proclamation that all of his majesty's ships must fly a union pennant. This distinction was further strengthened by a proclamation in 1674 which forbade merchant vessels from flying any pennants.<ref>{{cite book |last1=Perrin |first1=william Gordon |year=1922 |title=British Flags, Their Early History, and Their Development at Sea: With an Account of the Origin of the Flag as a National Device |url=https://archive.org/details/britishflagsthei00perrrich |publisher=Cambridge University Press archive |page=[https://archive.org/details/britishflagsthei00perrrich/page/202 202] }}</ref>

The system of numbering pennants was adopted prior to the [[First World War]] to distinguish between ships with the same or similar names, to reduce the size and improve the security of communications, and to assist recognition when ships of the same class are together.

During the First World War, pennant numbers were changed on a regular basis, with only those for ships in Home waters centrally controlled; those on foreign stations were allocated on a local basis. However, in November 1919 a new navy-wide system was introduced, with the intention that ships should now carry a permanent number. In most cases, plain numbers were given to capital ships and cruisers, and ones with flags-superior to smaller ships. While the numbers allocated to major warships (except for a few older vessels) would generally remain stable into the 1930s, destroyers were subject to further revisions, stability being reached in January 1922. While 1919/1922 numbers were allocated on a fairly systematic basis, later allocations were on the basis of re-allocating numbers made available by the disposal of older vessels. The next major revision took place in the late 1930s, when the volume of new construction was such that insufficient 'spare' numbers were now available for new ships. Accordingly, older cruisers had the flag-superior 'I' added in front of their existing plain numbers; as a result, submarines, which had previously used 'I', were given a new scheme of flags-inferior. Other changes  were also made at this time. The next major change took place in 1940, when there was a wholesale set of changes to flags-superior, including the old cruisers changing from 'I' to 'D'.<ref>{{cite journal |last1=Dodson |first1=Aidan |title=The Development of the British Royal Navy's Pennant Numbers Between 1919 and 1940 |journal=Warship International |date=2024 |volume=61 |issue=2 |page=134–66}}</ref>

Traditionally, a pennant number was reported with a [[full stop]] "." between the flag superior or inferior and the number, although this practice has gradually been dropped, and inter-war photos after about 1924 tend not to have the full stop painted on the hull. The system was used throughout the navies of the [[British Empire]] so that a ship could be transferred from one navy to another without changing its pennant number.

Pennant numbers were originally allocated by individual naval stations and when a ship changed station it would be allocated a new number. The Admiralty took the situation in hand and first compiled a "Naval Pendant List" in 1910, with ships grouped under the distinguishing flag of their type. In addition, ships of the 2nd and 3rd (i.e. reserve) fleets had a second flag superior distinguishing from which naval depot they were crewed: "C" for [[Chatham Dockyard|Chatham]], "D" for [[HMNB Devonport|Devonport]], "N" for [[Nore]] and "P" for [[Portsmouth]].

A completely new system was adopted in 1948, when flags-superior specific to a type of ship were introduced. For example, cruisers had the flag-superior 'C', destroyers 'D', frigates 'F' and carriers 'R'. In general, the existing numerical part of a ship's number was kept, except where this would lead to duplication (especially in the case of frigates, where 'F' now absorbed the former 'K', 'L' and 'U' lists), in which case the number was increased by 100, 200 or 300, as necessary.

The 1948 system was later taken over by NATO, and a single pennant list set up for all NATO navies, apart from the US and Canada.

During the 1970s, the service stopped painting pennant numbers on submarines on the grounds that, with the arrival of nuclear boats, they spent too little time on the surface, although submarines do continue to be issued numbers.

{{HMS|Lancaster|F229|6}} was initially allocated the pennant number F232, until it was realised that in the Royal Navy, form number 232 is the official report for ships that have run aground; sailors being superstitious, it was quickly changed to F229.

===Second World War=== 
<ref>{{cite book |last1=Lenton |first1=H T |title=British and Empire Warships of the Second World War |date=1998 |publisher=Greenhill Books |location=London |isbn=1-85367-277-7 |page=713–25}}</ref>

====No flag superior====
Pendant number 13 was not allocated.
* Capital ships, aircraft carriers, modern cruisers

====Flags superior====
Pendant numbers 13 were not allocated to flag superiors. The letters J and K were used with three number combinations due to the number of vessels.
* D — [[destroyer]]s (until 1940), older [[capital ship]]s, [[aircraft carrier]]s, [[cruiser]]s (from 1940)
* F — destroyers (until 1940) and [[Armed merchantman|large auxiliary combatants]] (from 1940)
* G — destroyers (from 1940)
* H — destroyers
* I — aircraft carriers, cruisers (until 1940), destroyers (from 1940)
* J — [[minesweepers]]
* K — [[corvette]]s, [[frigate]]s
* L — [[escort destroyer]]s, [[sloop-of-war|sloops]] (until 1941)
* M — [[minelayer]]s
* N — minesweepers
* P — sloops (until 1939), boom defence vessels (until 1940)
* R — destroyers (from 1942), sloops
* T — [[river gunboat]]s, netlayers
* U — sloops (from 1941)
* W — tugs and salvage vessels
* X — special service vessels
* Z — gate, mooring and boom defence vessels
* 4 — [[Auxiliary ship|auxiliary]] anti-aircraft vessels
* FY — fisheries (auxiliary [[fishing trawler]]s, [[drifter (fishing boat)|drifter]] etc.)

====Flags inferior====
Flags inferior were applied to submarines. Royal Navy submarines of the "H" and "L", and some transferred American vessels, were not issued names, only numbers. In these cases, the pendant number was simply the hull number inverted (i.e. ''L24'' was issued pendant "24L"). Pre-war photos show the pendants painted correctly, with the flag inferior, but wartime photos show that the numbers tend to be painted "backwards", in that the inferior was painted on as a superior. For obvious reasons, the inferior "U" was not used so as not to confuse friendly ships with [[Nazi Germany|German]] [[U-boat]]s. For similar reasons "V" was not used. Pendant numbers 00–10, 13, and those ending in a zero were not allocated to flag inferiors.
* A — allied (Polish [[ORP Orzeł (1938)|ORP ''Orzeł'' (85A)]])
* C ("coastal") — {{sclass2|U|submarine|4}} (pre-war construction)
* F ("fleet") — {{sclass2|River|submarine|4}}
* H — [[British H-class submarine|H class]]
* L — [[British L-class submarine|L class]]
* M ("minelayer") — {{sclass|Grampus|submarine|4}}
* N — allocated to existing submarines after 1940.
* P — [[Odin-class submarine|O class]], [[Parthian-class submarine|P class]]
** 31P— U class (wartime construction), [[British V-class submarine|V class]]
** 211P to 299P — [[British S-class submarine (1931)|S class]] (wartime construction)
** 311P to 399P— [[British T-class submarine|T class]]
** 411P to 499P— [[Amphion-class submarine|A class]]
** 511P to 599P— [[United States Navy]] [[lend-lease]] submarines
** 611P to 699P— commandeered foreign construction
** 711P to 799P— captured enemy submarines
* R — [[Rainbow-class submarine|R class]]
* S — S-class submarines (pre-war construction)
* T — T-class submarines (pre-war construction)

===Post-1948===
After the Second World War, in 1948, the Royal Navy adopted a rationalised "pennant" number system where the flag superior indicated the basic type of ship as follows. "F" and "A" use two or three digits, "L" and "P" up to four. Again, pennant 13 is not used (for instance the helicopter carrier {{HMS|Ocean|L12|3}} was followed by {{HMS|Albion|L14|3}}).
* A  — auxiliaries (vessels of the [[Royal Fleet Auxiliary]], [[Royal Maritime Auxiliary Service]], and [[Royal Navy Auxiliary Service]], including depot ships, boom defence vessels, etc.)
* C  — cruisers (currently none in service, therefore unused)
* D  — destroyers
* F  — frigate (former escort destroyers, sloops and corvettes)
* H  — shore signal stations (military); survey vessels
* K  — miscellaneous vessels (e.g., the helicopter support ship {{HMS|Lofoten|K07|6}} or the seabed operations vessels [[RFA Proteus|RFA ''Proteus'']] and {{HMS|Challenger|K07|6}})
* L  — amphibious warfare ships
* M  — minesweepers
* N  — minelayers (currently none in service, therefore unused)
* P  — patrol boats
* R  — aircraft carriers
* S  — submarines
* X  — experimental vessels (currently, the only vessel to use this is [[XV Patrick Blackett]] which is not a commissioned ship of the Navy but is crewed and run by the Royal Navy)
* Y  — yard vessels

===Flotilla bands===

====1925–1939====
From 1925, [[flotilla leader]]s were issued with but did not paint on pendant numbers. Instead, a broad band {{convert|4|ft|m}} deep was painted round their fore-funnel. Divisional leaders wore a pendant number and had a narrower {{convert|2|ft|m}} deep band on the fore-funnel, painted {{convert|3|ft|m}} from the top. The [[Mediterranean Fleet]] wore black leader bands and the [[British Atlantic Fleet|Atlantic]] – later [[Home Fleet]] wore white bands. The flotillas wore combinations of bands on their after funnel to identify them. From 1925 the following bands were worn;
* 1st Destroyer Flotilla — one black band
* 2nd Destroyer Flotilla — two black bands (one red from 1935)
* 3rd Destroyer Flotilla — three black bands
* 4th Destroyer Flotilla — no bands
* 5th Destroyer Flotilla — one white band
* 6th Destroyer Flotilla — two white bands
* 8th Destroyer Flotilla (from 1935) — one black and one white band

====Second World War====
When single funnelled destroyers entered the fleet with the [[J, K and N class destroyer|J class]] in 1939 and with an expansion in the number of flotillas, the system was changed accordingly. Single funnelled ships wore a {{convert|3|ft|m}} deep band as a flotilla leader. As a divisional leader they had a {{convert|2|ft|m}} wide vertical band the same colour as, and extending {{convert|6|ft|m}} below, the upper flotilla band. Leaders bands were white for Home Fleet, red for Mediterranean Fleet, and the system of flotilla bands changed to;
* 1st Destroyer Flotilla (Mediterranean) — 1 red, [[G and H-class destroyer|G class]]
* 2nd Destroyer Flotilla (Mediterranean) — 2 red, [[G and H-class destroyer|H class]]
* 3rd Destroyer Flotilla (Mediterranean) — 3 red bands, then none, [[I-class destroyer|I class]]
* 4th Destroyer Flotilla (Mediterranean) — none, [[Tribal-class destroyer (1936)|Tribal class]]
* 5th Destroyer Flotilla (Mediterranean) — none, [[J-, K- and N-class destroyer|K class]]
* 6th Destroyer Flotilla (Home) — 1 white, Tribal class
* 7th Destroyer Flotilla (Home) — 2 white, [[J-, K- and N-class destroyer|J class]]
* [[8th Destroyer Flotilla]] (Home) — 3 white, [[E and F-class destroyer|F class]]
* 9th Destroyer Flotilla (Home) — 1 black & 2 white, [[V and W-class destroyer|V and W class]]
* 10th Destroyer Flotilla (Home) — none, V & W class
* 11th Destroyer Flotilla ([[Western Approaches Command|Western Approaches]]) — 1 black over 2 red, V and W class
* 12th Destroyer Flotilla ([[Rosyth]]) — 1 white over 1 red, [[E and F-class destroyer|E class]]
* 13th Destroyer Flotilla ([[Gibraltar]]) — 1 white over 2 red, V and W class
* 14th Destroyer Flotilla (Home) — 1 red over 1 black, V and W class
* 15th Destroyer Flotilla (Rosyth) — 1 red over 2 black, V and W class
* 16th Destroyer Flotilla ([[HMNB Portsmouth|Portsmouth]]) — 1 red over 1 white, V and W class
* 17th Destroyer Flotilla ([[Western Approaches Command|Western Approaches]]) (from 1940) — 1 red over 2 white, [[Town-class destroyer|Town class]]
* 18th Destroyer Flotilla ([[English Channel|Channel]]) — 1 white & 1 black, [[A-class destroyer (1929)|A class]]
* 19th Destroyer Flotilla ([[Dover]])— 1 white over 2 black, [[B-class destroyer|B class]]
* 20th Destroyer Flotilla (Portsmouth) — 2 white over 1 black, [[C and D-class destroyer|C class]]
* 21st Destroyer Flotilla (China Station) — 2 white over 1 red, [[C and D-class destroyer|D class]]

Flotilla bands were used throughout the war although war-losses, operational requirements, and new construction broke up the homogeneity of the destroyer flotillas. Vessels were deployed as and when they were needed or available, and were often incorporated into mixed "escort groups" containing a range of vessel types such as [[sloop-of-war|sloops]], [[corvette]]s, [[frigate]]s and [[escort carrier]]s. A few of the escort groups adopted funnel bands; others (like the B7 escort group) wore letters on their funnels.

====Post-war====
Post-war Flotillas were no longer identified by bands, but by large [[cast metal]] numbers bolted to the funnels. Flotilla leaders continued to display a large band at the top of the funnel and half leaders would carry a thin black band around the funnel.

===Deck codes===<!-- This section is linked from {{HMS|Invincible|R05|6}} -->
Aircraft carriers and vessels operating aircraft have a deck code painted on the [[flight deck]] to aid identification by aircraft attempting to land. This is in a position clearly visible on the approach path. The Royal Navy uses a single letter (typically the first letter of the ship's name) for aircraft carriers and large vessels operating aircraft, and pairs of letters (usually letters from the ship's name) for smaller vessels. The [[United States Navy]], with its larger fleet, uses the numeric part of the [[hull number|hull classification number]] (a system analogous to pennant numbers). Deck codes used by contemporary major British naval warships include:
* HMS ''Albion'' — AN
* {{HMS|Bulwark|L15|6}} — BK
* {{HMS|Dauntless|D33|6}} — DT
* HMS ''Ocean'' — O
* HMS ''Ark Royal'' — R
* HMS ''Invincible'' — N
* HMS ''Illustrious'' — L
* {{HMS|Queen Elizabeth|R08|6}} — Q
* HMS ''Prince of Wales'' — P
* [[RFA Argus (A135)|RFA ''Argus'']] — AS
* [[RFA Lyme Bay (L3007)|RFA ''Lyme Bay'']] — YB
* RFA ''Cardigan Bay'' — CB
* RFA ''Mounts Bay'' — MB