Pennant Numbers, Royal Navy

The Royal Navy has used pendants to indentify its ships since the 17th century, but a modern pennant system did not properly come into existence until World War I though it was limited to smaller ships like destroyers, submarines, and smaller craft of which there were hundreds in commission and in the reserve fleets. The pennant system is composed of letter prefix, known as the flag superior, followed by a numerical suffix, known as the flag inferior. Before 1917, there was no standardized pattern for assinging either flag superior or inferiors. For example, some older and reserve ships were given a prefix based on their home port, such as Chatham (C), Devonport (D), Nore (N), and Portsmouth (P). Newer destroyers and submarines were given prefixes based on their squadron or class, respectively. For submarines the pennant number was often the reverse of their alpha-numerical name given that at the time they were not given proper names; thus the L-class submarine HMS L26 had its pennant number 26L. It was also common before 1917 to assign alphanumeric flag inferiors, which was likely as a result of the two character limitation which was not practical at a time when hundreds of ships were in service. In all cases, pennant number changes were frequent which added to the confusion over a ship's identity which was worsened by the fact that prefixes were usually assigned randomly per ship(except for submarines), and recycled when a ship was sunk or retired. For example, the V-class destroyer HMS Vanoc was known to have had the following pennant numbers throughout its almost 30-year career which spanned both world wars: F82A, F27, H4A, F84, and H33.

Attempts to create a more standardized pennant number system began in the later part of the war, from around 1917 onward. By now it was customary for destroyer-sized ships and smaller to have their their pennant numbers (usually just the flag inferior) on their hulls, which made indentification easier particularly when ships of a similar class where operating together. This practice was not taken with larger ships like battleships, cruisers, and aircraft carriers although by now they too had a pennant number (usually just a numerical flag inferior) assigned for signalling purposes. But by and large, similar ship types were given the same flag superior although destroyers and submarines remained the exception (see below). The outbreak of World War II resulted in major changes to the pre-war system, particularly as new types of ships were introduced such as amphibious vessels. Major changes to the pennant number system took place in December 1938 and particularly in May 1940 the latter which largely remained unchanged throughout the war. A peculiarity of the system was use of different flag superiors for older ship classes, this was likely as a result of the need to identify vintage, pre-war vessels from the newer types that were entering service in large numbers. Different flag superiors were also occasionally used for US-built ships provided via Lend-Lease such as escort carriers. Some interwar conventions remained, however, as as the lack of a flag superior for battleships, cruiser, and aircraft carriers, though there were a few exeptions. The two County-class heavy cruisers operated by the Royal Australian Navy as well as some of the older pre-war light cruiser classes used I and later D prefixes, as did the two light aircraft carriers HMS Hermes and HMS Argus and the three maintenance or utility carriers built (HMS Pioneer, HMS Perseus, and HMS Unicorn). Some ship types like corvettes now had three-digit suffixes which greatly expanded the range of unique numbers, but most others remained two-digit.

Destroyers and submarines had the most complicated pennant numbering patterns during World War II. Destroyers received different flag superiors based on their class, and at some point during the interwar years, the surviving World War I ships moved away from the complicated alpha-numeric flag inferiors into standard two-digit numeric pennants. These were assigned a D prefix in 1939, while those that were eventually converted into escort destroyers were assingned an L. Post-Washington Naval Treaty classes had somewhat simpler histories, with A- to D-class leaders receiving a D prefix which changed to I in May 1940. All other ships in the A- to H-classes received an H prefix which remained in place throughout the war. Tribal-class ships commissioned before December 1938 received an L prefix, but this was changed to F on that date. Likewise, the J- and K-classes (the last pre-war designs) also were given a F prefix. Both Tribal- as well as J-, and K-classes would change to a G prefix in May 1940. The G prefix became standard for all wartime classes up to the T-class, the exception being the R-class which reverted to the H-prefix (for reasons unknown; possibly because destroyers still had a two-digit limit). All destroyers from the T-class onward received an R prefix.

During the pre-war years, submarines retained their inverse pennant numbering scheme, where the alphabetic flag superior was placed after the numeric flag inferior. All pre-war classes received a unique letter suffix (usually the same as their class letter) with the exception of the O- or Odin-class which borrowed the P suffix, as well as the Thames- and Grampus-classes which used the F and M suffixes. All pre-war classes adopted the N suffix from December 1938, and this was turned into a prefix from May 1940. The S-, T-, and U-classes were somewhat more complicated as these were built in batches that corresponded to their build progammes. Pre-war programmes used the S, T, and C suffixes respectively, and like the other pre-war classes, were switched to N in December 1938 and to an N prefix in May 1940. Boats from the War Emergency Programme (which were completed in 1939-41) all began with an N prefix and this was retained throughout the war. Finally, all boats that were built from the 1940 Programme onward began with a P prefix, as did the subsquent V- and Amphion-classes of which all boats were built during wartime and afterward.

Flag superiors for coastal, support, and auxiliary ships is rather confusing given that the May 1940 changes affected numerous ship types. For a comprehensive list see www.niehorster.org.

The following table summarizes the pennant system used during the 1938-45 period which is applicable for all ships that were in service during World War II:

Ships assigned to the British Pacific Fleet (BPF) adopted a pennant number system that was closer to the US Navy's hull classification system. Flag superiors were assigned to all ships, with the same letter being used for all ships of the same type. However, the Royal Navy tradition of not painting pennant numbers on the hulls of battleships, cruisers, and aircraft carriers was respected. Flag inferiors were reassigned in a more orderly fashion and these replaced the random numbers assigned in normal Royal Navy service. All BPF ships reverted to their original Royal Navy pennant numbers after the war. The following is a list of flag superiors assigned for BPF ships:

After the war, there was a need to standardize the flags superior, particularly given the sheer number of new types of escort and amphibious ships that were introduced. For the first time in the Royal Navy's history, all ships of the same type would have an identical flag superior, and this was partly made possible due to the increase in digits to three in those flags that were previously limited to two (such as destroyers, which were given the D flag). Where possible, only the flag superior changed and the ship retained its pennant number. But where there was a conflict, the pennant number would be modified, usually by adding an extra digit. Thus destroyers HMS Wakeful went from R59 to D159 and HMS Wager went from R37 to D237. In some cases, the changes were more substantial but still relatively subtle such as HMS Tenacious switching from R45 to D44 and HMS Undine from R42 to R141. Interestingly, battleships remained without a flag superior and were simply known by their two-digit pennant numbers.

The Royal Navy eventually adopted the NATO pennant system which was itself based on the Royal Navy's 1948 scheme (with some alternations). NATO's pennant number system introduced consecutive numbering but this was not strictly applied by the Royal Navy until quite late. For example, the first British frigate class that featured consecutive numbering throughout all ships was the Amazon-class from the mid-1970s although some other ship types began earlier. The UK's assigned pennant number ranges within the NATO system were consistent with the numbering schemes applied in the 1948 scheme, which ran from 0-299. As a result, the Royal Navy did not need any adjustment to the new system and no ship required a new pennant number after the implementation of the NATO system. The few cases where UK ships did not conform to the assigned pennant number ranges, these were seemingly left intact (for example, a few War Emergency destroyers that were given numbers in the D200 range which was not a range later assigned to the UK).

See the NATO Pennant Numbers page for more information