Ships Pennant Numbers
Image: P281 is the pennant number for HMS Tyne, the first of the River Class offshore patrol vessels built for the Royal Navy.
The name ‘pennant number’ arises from the fact that ships were originally allocated a pennant (flag) identifying a flotilla or particular type of vessel: for example, in the Royal Navy, the red burgee for torpedo boats, H for torpedo boat destroyers. By the addition of a number to the identifying pennant, each ship could be uniquely identified. A pennant number thus consists of letters and numbers. Where a letter precedes a number it is known as a "flag superior" and where it is a suffix it is known as a "flag inferior". Not all pennants have a flag superior.
The system was adopted prior to World War One 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. 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 Pennant 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 manned; "C" for Chatham, "D" for Devonport, "N" for Nore and "P" for Portsmouth. Destroyers were initially allocated the flag superior "H", but as this covered only one hundred possible combinations from H00 to H99 the letters "G" and "D" were also allocated. When ships were sunk, their pennant numbers were reissued to new ships.
The flag superior for whole ship classes has often been changed while the numbers stayed the same. For example, in 1940, the Royal Navy swapped the letters "I" and "D" around (e.g. D18 became I18 and I18 became D18) and in 1948, "K", "L" and "U" all became "F", where there was a conflict, a 2 was added to the front of the pennant number.
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 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.
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 submarines
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 World War II, 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 current Ocean - L12 is 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
D — destroyers
F — frigate (former escort destroyers, sloops and corvettes)
H — hydrographic 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