Pennant number

Pendant number 13 was not allocated.

• Capital ships, aircraft carriers, cruisers

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 — destroyers (until 1940), capital ships, aircraft carriers, cruisers (from 1940)
• F — destroyers (until 1940) and large auxiliary combatants (from 1940)
• G — destroyers (from 1940)
• H — destroyers
• I — capital ships, aircraft carriers, cruisers (until 1940), destroyers (from 1940)
• J — minesweepers
• K — corvettes, frigates
• L — escort destroyers, sloops (until 1941)
• M — minelayers
• N — minesweepers
• P — sloops (until 1939), boom defence vessels (until 1940)
• R — destroyers (from 1942), sloops
• T — river gunboats, netlayers
• U — sloops (from 1941)
• W — tugs and salvage vessels
• X — special service vessels
• Z — gate, mooring and boom defence vessels
• 4 — auxiliary anti-aircraft vessels
• FY — fisheries (auxiliary fishing trawlers, drifter etc.)

Flag inferiors 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 German U-boats. For similar reasons "V" was not used. Pendant numbers 00–10, 13, and those ending in a zero were not allocated to flag inferiors.

• C ("coastal") — U class (pre-war construction)
• F ("fleet") — River class
• H — H class
• L — L class
• M ("minelayer") — Grampus class
• P — O class, P class
  • 31P— U class (wartime construction), V class
  • 211P to 299P — S class (wartime construction)
  • 311P to 399P— T class
  • 411P to 499P— A class
  • 511P to 599P— United States Navy lend-lease submarines
  • 611P to 699P— commandeered foreign construction
  • 711P to 799P— captured enemy submarines
• R — R class
• S — S-class submarines (pre-war construction)
• T — T-class submarines (pre-war construction)

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 Ocean (L12) was followed by Albion (L14)).

• 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 seabed operations vessel HMS Challenger or the helicopter support ship HMS Lofoten)
• L — amphibious warfare ships
• M — minesweepers
• N — minelayers (currently none in service, therefore unused)
• P — patrol boats
• R — aircraft carriers
• S — submarines
• Y — yard vessels

From 1925, flotilla leaders were issued with but did not paint on pendant numbers. Instead, a broad band 4 feet (1.2 m) deep was painted round their fore-funnel. Divisional leaders wore a pendant number and had a narrower 2 feet (0.61 m) deep band on the fore-funnel, painted 3 feet (0.91 m) from the top. The Mediterranean Fleet wore black leader bands and the 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

When single funnelled destroyers entered the fleet with the J class in 1939 and with an expansion in the number of flotillas, the system was changed accordingly. Single funnelled ships wore a 3 feet (0.91 m) deep band as a flotilla leader. As a divisional leader they had a 2 feet (0.61 m) wide vertical band the same colour as, and extending 6 feet (1.8 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 class
• 2nd Destroyer Flotilla (Mediterranean) — 2 red, H class
• 3rd Destroyer Flotilla (Mediterranean) — 3 red bands, then none, I class
• 4th Destroyer Flotilla (Mediterranean) — none, Tribal class
• 5th Destroyer Flotilla (Mediterranean) — none, K class
• 6th Destroyer Flotilla (Home) — 1 white, Tribal class
• 7th Destroyer Flotilla (Home) — 2 white, J class
• 8th Destroyer Flotilla (Home) — 3 white, F class
• 9th Destroyer Flotilla (Home) — 1 black & 2 white, V and W class
• 10th Destroyer Flotilla (Home) — none, V & W class
• 11th Destroyer Flotilla (Western Approaches) — 1 black over 2 red, V and W class
• 12th Destroyer Flotilla (Rosyth) — 1 white over 1 red, 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 (Portsmouth) — 1 red over 1 white, V and W class
• 17th Destroyer Flotilla (Western Approaches) (from 1940) — 1 red over 2 white, Town class
• 18th Destroyer Flotilla (Channel) — 1 white & 1 black, A class
• 19th Destroyer Flotilla (Dover)— 1 white over 2 black, B class
• 20th Destroyer Flotilla (Portsmouth) — 2 white over 1 black, C class
• 21st Destroyer Flotilla (China Station) — 2 white over 1 red, 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 sloops, corvettes, frigates and escort carriers. A few of the escort groups adopted funnel bands; others (like the B7 escort group) wore letters on their funnels.

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.

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 classification number (a system analogous to pennant numbers). Deck codes used by contemporary major British naval warships include:

• HMS Albion — AN
• HMS Bulwark — BK
• HMS Dauntless — DT
• HMS Ocean — O
• HMS Ark Royal — R
• HMS Invincible — N
• HMS Illustrious — L
• HMS Queen Elizabeth — Q
• HMS Prince of Wales — P
• RFA Argus — AS
• RFA Lyme Bay — YB
• RFA Cardigan Bay — CB
• RFA Mounts Bay — MB

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 vessel.

Albion class

• HMS Albion — AN
• HMS Bulwark — BK

River class

• HMS Forth — FH
• HMS Medway — MY
• HMS Trent — TT
• HMS Tamar — TM
• HMS Spey — SY

Daring class

• HMS Daring — DA
• HMS Dauntless — DT
• HMS Diamond — DM
• HMS Dragon — DN
• HMS Defender — DF
• HMS Duncan — DU

Duke class

• HMS Argyll — AY
• HMS Lancaster — LA
• HMS Iron Duke — IR
• HMS Monmouth — MN
• HMS Montrose — MR
• HMS Westminster — WM
• HMS Northumberland — NL
• HMS Richmond — RM
• HMS Somerset — SM
• HMS Sutherland — SU
• HMS Kent — KT
• HMS Portland — PD

Invincible class

• HMS Invincible — N
• HMS Illustrious — L
• HMS Ark Royal — R

Queen Elizabeth class

• HMS Queen Elizabeth — Q
• HMS Prince of Wales — P

Bay class

• RFA Cardigan Bay — CB
• RFA Lyme Bay — YM
• RFA Mounts Bay — MB

Tide class

• RFA Tidespring — TS
• RFA Tiderace — TR
• RFA Tidesurge — TU
• RFA Tideforce — TF

Individual ships

• HMS Ocean — O
• RFA Argus — AS
• RFA Fort Victoria — FV

De Zeven Provinciën class

• HNLMS De Zeven Provinciën — ZP
• HNLMS Tromp — TR
• HNLMS De Ruyter — DR
• HNLMS Evertsen — EV

Holland class

• HNLMS Holland — HL
• HNLMS Zeeland — ZL
• HNLMS Friesland — FR
• HNLMS Groningen — GR

• HNLMS Rotterdam — RD
• HNLMS Johan de Witt — JW
• HNLMS Karel Doorman — KD

Halifax class

• HMCS Halifax — HX
• HMCS Vancouver — VR
• HMCS Ville de Québec — VC
• HMCS Toronto — TO
• HMCS Regina — RA
• HMCS Calgary — CY
• HMCS Montréal — ML
• HMCS Fredericton — FN
• HMCS Winnipeg — WG
• HMCS Charlottetown — CN
• HMCS St. John's — SJ
• HMCS Ottawa — OA

• ENS Anwar El Sadat — AS
• ENS Gamal Abdel Nasser — GN
• ENS Tahya Misr — TM
• ENS El Fateg — FT

Braunschweig class

• Braunschweig — BS
• Magdeburg — MD
• Erfurt — EF
• Oldenburg — OL
• Ludwigshafen am Rhein — LR

Sachsen-class frigate

• Sachsen — SN
• Hamburg — HA
• Hessen — HE

Auxiliary ships

• Main — MA
• Mosel — MO

Charles de Gaulle aircraft carrier

• FS Charles de Gaulle - G

Mistral class

• FS Tonnerre — TO
• FS Dixmude — DX
• FS Mistral — MI

Horizon class

• FS Forbin — FB
• FS Chevalier Paul — PL

Aquitaine class

• FS Aquitaine — QN
• FS Provence — PC
• FS Languedoc — LD
• FS Auvergne — VG
• FS Bretagne — BT

La Fayette class

• FS La Fayette — YE
• FS Surcouf — SF
• FS Courbet — CO
• FS Aconit — AT
• FS Guépratte — GT

• HMNZS Otago — OTA
• HMNZS Canterbury — CAN

Vasco da Gama class

• NRP Vasco da Gama - VG
• NRP Corte Real - CR
• NRP Álvares Cabral - AC

Bartolomeu Dias class

• NRP Bartolomeu Dias - BD
• NRP Dom Francisco de Almeida - FA