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Destroyer HMS Ivanhoe, Flag D - D16 (Navy Photos, click to enlarge) return to Lt-Cdr Mason's researches
or World War 2, 1939-1945

 by Geoffrey B Mason, Lieutenant Commander, RN (Rtd) (c) 2007

History and Development


As early as 1350 records show that an order was issued relating to the use of a flag by Admirals. It indicated that when the Admiral wished to assemble the Captains and Masters of the Fleet he was to 'carry a Banner of Council high in the middle of the mast of his vessel'. A further direction was made in 1653 relating to the use of flags 'for the better ordering of the Fleet in fighting'. Official instructions on this subject were subject to the normal administrative delay - in this case some 46 years! Further progress in this matter was evident in 1778 when Lieutenant Sir Charles Knowles submitted to the Admiralty a proposal for a 'Signal Book'. This officer continued to show a keen interest in the subject for many years. The first Fleet Signal Book was issued in 1799. Various up-dates were made to it amongst which was the use of combinations of flags for special phrases in common usage and more significantly similar combinations to allow individual ships or formations of ships to be identified.



Senior Officers' Ships


The identification of a Senior Officer's ship in the Royal Navy was originally made by her wearing a flag of the same colour as that used for the name of the Squadron - Red, White or Blue. However, in 1864, when the use of squadron colours ceased, the White Ensign was adopted for all HM Ships and a change became necessary. It was 1898 before a standard procedure was adopted and since that date Flag Officers' ships have been identified by use of a St George's Flag with the addition of one or two Red Balls except for ships with an Admiral of the Fleet or a full Admiral embarked. In those two cases a Union Flag or a plain St George's Flag respectively were used. A Vice Admiral used one Red Ball sited in the upper canton at the hoist (originally in the bottom canton). For a Rear Admiral an additional Red Ball was added in the bottom canton next the hoist (originally in both the bottom cantons). A Commodore's ship wore a Broad White pendant with the Cross of St George. These are all currently in use.



International Code of Signals


An International Code of Signals intended for use of merchant ships of all nationalities was proposed by the author Captain Maryatt in 1817. The Board of Trade gave approval for this innovation to be used in British ships in 1857 and further changes were made forty years later. These introduced the use of a set of four flags in a unique combination to identify individual ships. It is still used by merchant ships and warships for identification purposes.


Two sets of flags have, therefore, evolved for general signalling use - the International Code of Signals and a Naval Code. Both are carried in HM Ships and used for individual identification.



Types of Flag


Both codes include three basic types of bunting. These are rectangular, triangular or tapered shapes. The tapered form is known as a Pennant (or Pendant) and is predominantly used to indicate numbers. There is a variation of the triangular flag with a 'swallow tail' - known as a Burgee. In HM Ships the flags mainly used for identification are either a set of numerals or a set comprising a single alphabetic flag and two or three numerals. If the alphabetic flag in such a combination is hoisted before the numerics it is known as a flag superior and if after the numerics it is a flag inferior. This arrangement makes up the pennant number allocated to every British warship and auxiliary for identification purposes. Certain additional flags have special functions but some of these can be used as an alternative for a flag superior in a pennant number, eg, the 'fishery pennant'.



Jane's Fighting Ships System of Ship Identification 1909 to 1914


Reference is made in the 1909 and 1914 editions of this publication to the proposed use of a uniform system of identification of war­ships. It is suggested that users of the book, which was of inter­national significance, should use a sequence of two alphabetic characters for this purpose. The first was to show the type of warship and the second to indicate the number of masts and funnels for the Type quoted. The entry included instructions under an entry 'Fighting Ships Identification of Warships Signal System' describing the method of use. The primary purpose suggested was for use by merchant ships employed as 'war-scouts' and which did not carry any naval personnel embarked. Details of various hoists using the International Code of Signals together with standard 'shapes' were provided with examples of the sequence in which these were to be hoisted. Large merchant ships belonging to various countries were also included in this system. It is not clear whether this proposal ever had any official recognition but it might be conjectured that the use of class letters on the structure of destroyers before 1914 was influenced by this philosophy.



Allocation of Pennant Numbers


All HM Ships have used some kind of code flag identity in visual signalling for at least a century but these identities have only been physically marked on their structure since about 1910. Photographic evidence before that date suggests that a large number of torpedo boat destroyers (TBD) and destroyers had an alphabetic character painted on their hulls and in some cases also on their forward funnels. The character used was that of the 'class' of destroyer. Other methods also evident were the use of bands painted on funnels and in the case of submarines either a number alone or the 'class' letter alone painted on their conning towers.


Destroyers of classes 'A' to 'M' occasionally had numbers marked no their bow structure but this does not seem to have been universally adopted. Between 1910 and 1914 use of these markings became more common and sometimes was related to their home ports (D - Devonport; N - Nore and P - Portsmouth) but the format used was not standard in all ships. The formats varied considerably as some destroyers had pennant numbers with two alphabetic characters, eg, HA6 (HMS BOXER 1914-1915), HC7 (HMS BULLDOG 1918 changed to HC4 till 1919 when H25 was allocated). Others were the same as now adopted with an alphabetic flag superior with two numeric, eg, D01 (HMS ARAB 1914 - 1917 when H08); P14 (HMS ALBACORE 1914 till 1915 when changed to D76 and later to D01 in 1918).


By 1924 firm control on a universal basis within the whole navy, including those of the Dominions, had been established. These hull markings were, however, confined to destroyers and some smaller craft, such as, ML's, CMB's and submarines. Flotilla Leaders had no markings of pennant numbers but had a black band on their forward funnel. Hull markings enabled individual ships to be easily identified visually, particularly when several ships of the same type were in company. They were used for visual signalling purposes to identify an addressee. Throughout the period 1900 to 1924, capital ships, aircraft carriers, cruisers and large auxiliaries, such as depot and repair ships, had no hull markings but they each had a pennant number allocated for signalling use. In some cases these types of vessel were allocated a flag superior but not in the case of capital ships. There were many alterations to the allocations made in order to accommodate increases in the number of ships before, during and after World War One. In more recent times the wide­spread use of voice communication has reduced the use of visual signalling except where radio silence is in force. The current practice of use of a separate 'radio callsign' which is frequently changed to ensure security has reduced the need for a fixed identity. Nonetheless, pennant numbers are still displayed on hull structures of HM Ships and auxiliaries. This allows speedy identification of ships operating together or when in the vicinity of naval bases when they fly the appropriate identification flags. Hull markings also assist merchant ships wishing to make contact by visual signalling with warships.


In time of war the display of pennant numbers may be dispensed with, as was the case during the Falklands war. During that conflict RN Type 42 destroyers had a distinctive marking painted on their hulls to indicate clearly their nationality, because Type 42's were also used by the Argentine Navy. Submarines ceased to display markings on their structure during World War Two and this practice has basically been continued to date. In the case of other types of British warship, however, the use of hull markings has been considerably extended since the late 1950's. All HM Ships and auxiliaries now have their pennant numbers clearly shown on their hulls in a standard position.



Outline of the evolution of pennant numbers since 1917


1917 to 1920


This period is marked by the introduction of a standard system for all ships with particular regard to the flag superior allocated to individual types of ship and to the physical location of the hull markings. Flags ‘G’ and ‘F’ were allocated to new destroyers. Older destroyers continued to use Flag ‘D’ and Flag ‘H’ and there were very frequent changes of allocation. Flag 'I' was allocated to all new cruisers such as the 'C' and 'D' classes then joining the Fleet. Flag 'P' was used only for patrol vessels.


1920 to 1935


A very significant reduction in the numbers of destroyers made a reappraisal necessary and earlier identities were superseded by flags 'D' and 'H' only. At this period flag 'N' was allocated to survey ships and flag 'T' to river gunboats. Changes were also made in the case of submarines which had a combination of alphabetic flags superior and inferior to numerics but these were gradually standardized and only an alphabetic superior used. Some cruisers were also subject to change and used flag 'I' superior. No changes were introduced for capital ships, which continued to use numeric identities.


1935 to 1940


Corvette HMS Alisma, Flag K - K185 (NP/Mike Pocock)


The extent of new construction made it necessary to review the arrangements for pennant numbers. In particular, allowance had to be made for the large number of escorts, eg, Hunt class and Flower class, and Tribal class destroyers about to join the Fleet. The initial allocation of flag 'L' to the Tribal class was short-lived and this altered to flag 'F' allowing flag 'L' to be restricted to escorts only and to existing patrol sloops. A new identity (flag 'K') replaced the first choice of flag 'M' for all Flower class corvettes. The use of Armed Merchant Cruisers was anticipated by allocation of flag 'I' for these as well as its existing function for some cruisers.


1940 to 1945


Escort carrier HMS Reaper, Flag D - 82 without the "D" (NP/Mark Teadham)


Experience gained during the first few months of the war showed the earlier changes fell short of the needs of the greatly expanded fleet and more changes were desirable for security reasons. The were:


Destroyers – Flag ‘D’ and Flag 'F' replaced by flag 'I' and Flag 'G'. Flag 'R' was added later in 1943 for use by new fleet destroyers.


Submarines - All existing changed to flag 'N' and new to Flag ‘P’. No submarine had hull markings


Escort Sloops - Flag 'L' replaced by Flag 'U'.


Ex-US Coastguard vessels only Flag 'Y' and KIL class escorts (US build) used flag '5' superior.


Minesweepers - Fleet minesweepers and new construction Flag 'J' instead of Flag 'N'. This did not apply to trawlers and other ships used for this purpose which used a variety of identities.


Escort carriers- New escort carriers (mostly of US build - Biter class) were allocated Flag 'D'.


Coastal Forces - The new MGB's and MA/SB were allocated Flag 'S’ and ML's used flag 'Q’.


Landing Ships - Another large new group not previously needed. These used flag 'F’ and some flag 'A’.



1945 to 1958


frigate HMS Loch Insh, Flag F - F433 (NP)


The situation faced after the end of hostilities was similar to that in 1918. It was clearly necessary to reduce the number of different flags superior in use and to fill up gaps in any existing allocations for individual flags due to losses and cancellations. 

Destroyers - Flag 'D’ reintroduced and number of numerics increased to three. (Note: The use of three numerics had been commonplace during WW2 e.g. Flag K for FLOWERS.)


Escorts - Flag 'F’ reintroduced for all ships of Frigates size, and some frigates later designated as such in 1957. Numerics increased to three (in lieu of flags 'K' and 'L'.)


Submarines - Flag 'S’ except for few Flag 'N' soon to be removed from service. Up to three numerics used.


Minesweepers - Flag ’M’ replaced Flag ‘J’ and numerics increased. See below.


Survey Ships - Reclassified as Auxiliaries and allocated Flag ‘A’


These changes also allowed for commonality between European NATO navies. A standard flag superior was allocated for each type of ship. For that reason four digit numbers became common for ships, such as minesweepers. US Navy ships did not conform to these allocations.


1959 to Date


The predominant feature of this period for RN ships is the use of hull markings on all classes of warships and auxiliaries. RN cruisers and aircraft carriers for the first time had their pennant numbers painted on their hulls and used flag 'C' and flag 'R' respectively. Other changes included the introduction of flag 'K' for the Seabed Operations Vessel HMS CHALLENGER and the Helicopter Training Vessel RFA ENGADINE. For a short period submarines showed a hull marking of their pennant number but this practice has now ceased. There are wide disparities in the sequence of allocation of numbers particularly for minesweepers and landing craft to allow for international use within NATO. All auxiliaries continue to have their pennant numbers marked on the structure in the same way as warships.







from Dave Mallinson


Dave Mallinson's email of 7 February 2008:


"I have been conducting research into the allocation and operational use of a separate range of pennant numbers allocated to Royal Navy, Commonwealth and Allied warships (excluding those belonging to the USN) operating in the Indian and Pacific Oceans during 1944-45 as well as to the multitude of vessels that were allocated to the Fleet Train and allocated for harbour duties. These alternative pennant numbers are not fully documented, although individual examples can be found in published works such as 'Royal Navy Escort Carriers' (Hobbs) and a few photographic records exist show vessels carrying these numbers. The photographic record though is very sparse and it would appear that few of the ships operating in those theatres actually carried the pennants allocated to them.


I was advised that the source publication may have been the US Navy publication DNC 4A (Visual Call Sign Book) dated 1944 as corrected by various NRPMs up to 1946 but despite exhaustive searches in the UK, Canada and the US I have been unable to find an archived copy of this publication. The US National Archive did locate a copy DNC 4 dated 1942 but unfortunately this predates the introduction of this range of pennant numbers and so is of no help. The Naval Historical Branch and the Royal Navy Museum have also been unable to locate a copy of this publication. Another source suggest that BR 619 may provide details but again I have been unable to find a copy of this publication dating to later than 1942.


A incomplete list of these alternative pennant numbers appeared in the Warship Journal No. 107 Winter 1991 edition and although I have not seen a copy of this journal I am told that it included reference to DNC 4A. I can only presume that at some stage a copy of this publication was located and it provided the author with the details that were subsequently published. I have also beeen told that the late Arnold Hague worked on such a list a number of years ago and my contact suggested that as he had established links with the Naval Historical Branch his source of information may have originated from that source.



Which brings me on to the information you published on the subject of pennant numbers that appears on the Naval-History.Net web site. There is no mention of these numbers and I would be grateful if you can add anything on the subject. In particular my work on this subject started as I was asked to try and identify a vessel that had been photographed (above) alongside HMS STRIKER (D12, R.315 and A.468) which was operating in the Pacific in 1945. The vessel is obviously a Modified Black Swan Class but I can find no reference to the pennant number  which she is carrying. As you will be aware this class normally were allocated flag superior 'U' pennants and for those allocated to the war against Japan they were subsequent allocated Flag Superior 'B' pennants. There is also a picture of HMS WHIMBREL (U29) taken while at Manus in 1945 and showing her carrying her alternative pennant number B.278." (Following.  Dave does not know who owns copyright of either. Please click to enlarge.)





Brief reply from Gordon Smith:


"This is a subject that interests and puzzles me. I have Lenton's "British Empire Ships", which lists pennant numbers, but it is still not easy to understand the logic. With your permission, I would like to include your email and any subsequent emails with Geoff Mason as an Addendum to the Pennants page on It will add to the debate."



Dave's follow-up email:


"This subject really is one that has escaped under the radar and although over a period of time I have managed to gather together a list of these pennant numbers I know it is not complete. For example A.468 is missing from the list and I would also wish to locate the source document, or publication, to verify the list and provide absolute proof of identity for the few ships I have seen photographed carrying these alternative pennant numbers. The photographs of HMS WIMBREL and Modified Black Swan A.468 are interesting as they provide evidence, along with a small select group of other surviving photographs, of the existence of the alternative pennant numbers. 


I have not seen a copy of Lenton's 'British and Empire Warships of the Second World War'  but I expect it lists the standard Admiralty pennant numbers with all the changes that were made to the Flag Superior for certain class of warships over the period of the war. I very much doubt if it lists the pennant numbers allocated to units that were earmarked to join the Eastern and British Pacific Fleets. As an example, and for information I have listed the pennant numbers carried by the 'R' Class destroyers giving both their official Admiralty pennant number and also the alternative pennant number which I understand were allocated to them c.1945. 

Racehorse H.11 and D.37

Raider H.15 and D.38

Rapid H.32 and D.39

Redoubt H.41 and D.40

Relentless H.85 and D.41

Rocket H.92 and D.42

Roebuck H.95 and D.43

Rotherham H.09 and D.44

These Flag Superior 'D' pennant numbers do not, as far as I am aware, feature in any published works and the same applies to the vast majority of the pennant numbers that appear on this list.


Some of the Flag Superior 'R' pennant numbers allocated to the escort carriers do appear in the recently published 'Royal Navy Escort Carriers' (Hobbs) but not all of them and of course the Flag Superior 'R' pennant numbers allocated to the Fleet and Light carriers do not appear anywhere.


As you mention, the subject of pennant numbers, when looked at from their introduction prior to the First World War through to changes implemented post Second World War, is rather puzzling and made even more so by the lack of information relating to the pennant numbers that I am researching and also the changes introduced between the wars which is yet another forgotten subject.


Finally I could start to debate the reason for their introduction but until the source publication or document is identified any such debate would be unlikely to provide a definitive answer however my earlier reference to DNC 4A may give a pointer towards it being a US Navy inspired change and this may account for its apparently rare use by vessels operating in the Far East and Pacific theatres."



Geoff Mason's reply:


Pennant Numbers allocated to BPF ships for use during 1944-5 by RN ships operating with USN.


"My Article in WARSHIP Supplement No. 99 makes no mention of these since I was then unaware of their existence. Whether or not the later Article by Peter R Haack in No 107 was influenced by my work I do not know. I agree that Haack’s Article is incomplete and does not include any reference to Sloops nor to A Flag Superior identities which clearly existed.


The photograph of a Modified BLACK SWAN Class Frigate at Manus in 1945 certainly suggests that the B Flag Superior number may have been allocated to her at the time USN Numbers were being used by RN ships deployed with the USN.


Admiralty S-Series Admiralty Fleet Orders held by the Naval Historical Branch is the only place I know would be likely to promulgate the introduction of  USN Pennant Numbers to the Fleet. My best suggestion is that you contact them for information on S Orders  during 1944..


As for CVE allocations, British Pennant Numbers with Flag D were allocated to CVE's and were shown on some  photographs

in Hobb's book, eg AMEER, CHASER and several others.


The allocation of both RN and USN Pennant Numbers is recorded in Hobbs book on Page 184, pages 713/714 but incompletely in Lenton's BRITISH EMPIRE WARSHIPS, as well as  the USN identities in Haack’s Article."



Dave Mallinson, 25 February 2008:


I have now started to investigate any possibility that the data may be found in Admiralty ‘S’ Series Admiralty Fleet Orders.


Regarding Geoff Mason's comment "British Pennant Numbers with Flag ‘D’ were allocated to CVE and were shown on some CVE photographs in Hobbs. book, e.g. AMEER, CHASER and several others." This is correct and photographs usually show the RN Escort Carriers carrying the number only and missing off the 'D' Flag Superior.


There are however a very limited number of photographs of RN Escort Carriers carrying the alternative BFP pennant numbers. These vessels were allocated Flag Superior 'R', as were the Fleet Carriers, but intriguingly there is also a photograph of HMS SLINGER (D26), which was also allocated the alternative Pennant Number R313, carrying the Pennant Number A452. A second example shows HMS RULER (D72), allocated the alternative Pennant Number R311, carrying the Pennant Number A731.


I also believe HMS STRIKER (D12 and R315) may have been allocated Pennant Number A460 but unfortunately I have not found any photographic proof that this pennant number was carried by this vessel.


I am also not sure that I agree that the pennant numbers were directly associated with the US Navy system ("may have been allocated to her at the time USN Numbers were being used by Numbers to RN ships deployed with the USN" - Mason 111415Z Feb). The US Navy system was, and still is, based on hull numbers and indeed when I spoke to the US Navy Historical Branch they were also not clear if there was any association between the US Navy Hull Numbers and the British, Commonwealth and Allied navies use of the alternative pennant numbers carried by vessels operating in the Indian and Pacific Oceans during 1945. For example US Navy practise for the Carriers was to give them hull number starting with the letter 'C' for example CV 9 - ESSEX, CVL22 - INDEPENDENCE and CVE9 - BOGUE. Our Fleet, Light and Escort Carriers were all allocated Flag Superior 'R' pennant numbers. Certainly the Flag Superior 'B' pennant numbers were allocated to a wide variety of vessels ranging from Battleships, Frigates, Sloops, Minesweepers, Oilers, Tugs, Harbour Craft, and even Harbour Defence Motor Launches as well as merchant vessels working with the Fleet Train. This, as far as I can see, bears no relationship to the hull numbering system adopted by the US Navy. It is however quite possible that the introduction of this alternative numbering system had some link with the inter co-operability of the Allied naval forces with the US Navy operating in the Pacific theatre but apparently this was a connection did not extend to inter co-operation between these navies operating in other theatres during the war.


It is good to see other photographs of RN destroyers carrying one the alternative pennant numbers, in this case the photographs are of: -






The pennant number of the destroyer shown in the photograph (Day of days", destroyer steams alongside to transfer mail at sea during rest days, Formosa 1945. Also a Z or C-class) is, unfortunately, unreadable in its present state but to date I have not identify any alternative Flag Superior 'D' pennant numbers allocated to 'Z' Class destroyers, although many of the 'C' Class are documented. Indeed as far as I am aware none of the 'Z' Class left home waters before the end of the war. In the case of the 'C' Class only the CA's were sent to the Pacific Fleet. However the photograph may show one of the 'W' Class, which also operated in the Pacific, as these were also completed with the tall lattice foremast and short pole mainmast carried by the destroyer in the photograph.


Regarding the identity of the destroyer appearing to carry the pennant Number G39. The destroyer in the photograph is obviously one of the 'O' or 'P' classes fitted with the Mk V range finder with combined 285 RDF and the 4" Mk V guns on single MK III HA mountings, but crucially she is also fitted as a minelayer. Only four of the 'O' class were so fitted, HMS's OPPORTUNE, ORWELL, OBEDIENT and HMS OBDURATE (G39). The four were fitted out as minelayers as they enter service from late 1942 onwards. None of the 'P' Flotilla were fitted as a minelayer but surviving units of that class were sent to the Pacific whereas the O' Class served in the Home fleet for the duration of the war.


The photograph was therefore taken post Autumn 1942 and during a period when weather conditions allowed the men on the upper decks to be dressed in shorts and vests suggesting the ship was photographed operating either in warm waters or at least it was a warm day. The camouflage scheme worn by this destroyer does not support the idea that the photograph was taken later in the war. The disruptive camouflage schemes were abandoned in favour of the standard light tone designs and in particular the light grey shade with blue panel adopted by ships serving in the Indian and Pacific Oceans late in the war. This scheme is well demonstrated by the photographs of HM destroyers QUADRANT, WAGER and TENACIOUS.


So it is possible that whilst it was thought that the photograph was taken in the Pacific, thus ruling out the possibility that the destroyer could be HMS OBDURATE, it is indeed definitely HMS OBDURATE (G39). This ship was commissioned in September 1942 and then torpedoed and damaged on 25 January 1944 so this sequence of events would point, if the vessel in the photograph is OBDURATE, to the photograph dating from 1943.


In August 1943 HMS OBDURATE, along with sister ships HMS's OBEDIENT and OPPORTUNE escorted the damage carrier HMS INDOMITABLE to Norfolk, Virginia for repairs and it would therefore appear the photograph shows HMS OBDURATE alongside HMS INDOMITABLE during this voyage.


Incidentally the River Class frigate HMS PARRET (K304)shown in one of the other photographs was allocated the alternative pennant number B273 but, not unusually, she retains her original number in the photograph.

return to Lt-Cdr Mason's researches
or  World War 2, 1939-1945

revised 1/12/10