[U-190]

Originally Posted by gap

Recently I have been digging on the internet for information on the ensigns worn by various types of British and Commonwealth vessels, and I thought I would share my findings here in case someone is interested.

• Commonwealth merchant vessels
  Looking into Lloyd's records of merchant ships owned by Commonwealth steamship companies, I was surprised to discover that all of them were registered as British-flagged ones, no matter if their companies were actually based in the UK or not.
  
  The 2,053-ton bulk carrier Magog, for example, was owned by Canada Steamship Lines, a Montreal-based shipping company. As expected, uboat.net reports the ship as Canadian but convoyweb.org and, more importantly, the 1939 Lloyd Register have her as British. I have checked many other Canadian, Australian, New Zealand, etc. vessels, and they all were registered as British. As far as I can see there are two possible explaination to that:
  
  
  1. all the merchant vessels of the Commonwealth wore the Red Ensign;
     
     
  2. vessels belonging to (former) British colonies wore the Red Ensign (optionally) defaced with each country's national emblem, but Red Ensign variants were still officially considered (and registered) as British flags.
  
  In order to investigate the veracity of the last point I have checked many photographs. Discernig small flag details based on pictures which usually have a poor resolution is not so easy, nonetheless I think I have found a few photographs which seem to confirm my hypothesis.
  
  
   

  
  The picture above and the one below portray the Morialta and the Ulooloo respectively, both owned by Adelaide Steamship Company
  
  
   

  
  Both vessels have a Red Ensign hoisted on the flagstaff. The Union Jack on flag's canton is easily discernible, but can you see the white spot beneath it? Well, I am not 100% sure, but that might be one of the stars defacing the Australian Red Ensign
  
  One last picture, this time of the Princess Marguerite, a passenger ferry managed by British Columbia Coast Steamships, a division of the Montreal-based Canadian Pacific Railway Company
  
  
   

  
  Again, a brighter spot is barely discernible; that migh be the bottom portion of the coat of arms defacing the Canadian Red Ensign
  
  
• Catapult Aircraft Merchant ships/Merchant Aircraft Carriers
  Those were merchant vessels, owned by the Ministry of War Transport but managed by private companies and commanded/crewed by civils, threfore the regular civil (red) ensign was flown aboard them.
  
  
• Armed Merchant Cruisers
  They were merchant ships requisitioned by the Admiralty and commissioned in the Royal Navy for convoy defense. They were given the HMS prefix and, as any other naval vessel, they wore the White Ensign.
  
  
• Royal Fleet Auxiliary ships
  Mostly oilers, depot ships, fleet tenders, etc, either purpose-built or requisitioned for that purpose. They were commanded and crewed by members of the Royal Naval Reserve, they were given the RFA prefix and they wore the Admiralty Blue Ensign (former Transport Ensign): a Blue Ensign defaced with a horizontal yellow anchor.
  
  Source: http://www.historicalrfa.org/archive...ign-of-the-rfa
  
  
• Q-ships
  Basically heavily armed AMCs in disguise.
  
  
  
  Source: http://www.historicalrfa.org/rfa-cha...ip-information
  
  
• Royal Mail Ships
  A number o merchant vessels, especially ferries and ocean liners, were given the RMS prefix and designated to carry mail under contract to the British Royal Mail.
  The Flags of the Word project lists a Royal Mail Blue Ensign and the National Maritime Museum of Greenwich has one of these ensigns in its collection. Apparently this flag was worn by RM ships after 1902, but I ignore wether it was still in use at the oneset of WWII, when most RM ships were requisitioned as troop transports and swithched to other flags.
  
  
• Hospital Ships
  During WWII the Ministry of War requsitioned a number of private-owned ocean liners for use as hospital ships. The appearance of those vessels was regulated by the Hague Convention of 1907 and subsequent international agreements.
  
  
  
  source: https://ihl-databases.icrc.org/ihl/0...2563cd00424636
  
  Summing up, the general rule for hospital ships was to fly their national ensign "in its usual place" (i.e. at ship's stern while underway) + red cross flag on the mainmast "as high as possible" + the national ensign of the concerned belligerent if the ship belonged to a neutral country.
  
  Now the matter is: which was the ensign used aboard Commonwealth hospital ships? The following document (p. 7, fig. 9), gives a contradictory answer:
  
  https://maritimearchaeologytrust.org...-Burns_WEB.pdf
  
  The flag shown in fig. 9, p. 7 is a Board of Trade Blue Ensign, yet the caption reads: HMHS Lady Connaught Flag: “A Blue Ensign Flat”.
  
  A thread on Great War Forum sheds some light on the issue:
  
  
  
  The text above is relative to WWI, nonetheless a similar restriction to the one of 1914 was issued in 1939 ("All Blue Ensign warrants were cancelled in 1939"), so it is unlikely for Britsh hospital ships of WWII to have flown the "Blue Ensign flat". Instead of that, the probably following the WWI usage of the Transport Ensign, or they might have switched to the Board of Trade Ensign.
  
  
  Infantry landing ships
  According to Wikipedia (mentioning as reference: Bruce, Colin J. Invaders, Chatham Publishing, London, 1999 ):
  
  
  
  
• Troop transports
  Here I wish we had more information. The one source I have found so far is a comprehensive study on British ensigns published in 2015
  
  Among the other flags, it mentions (at p. 29):
  
  
  
  Whether the usage of the Board of Trade Blue Ensign started in the 20's lasted until WWII or not is a mystery to me, but it is likely that, similar to infantry landing ships, some troopers manned by civilian crews might have flown the Red Ensign.
  

Summary of the flags mentioned in this post and their usage:

Merchant vessels / Some troop transports (?) / Some Landing Ships / CAM/MAC ships
British Red Ensign *

As above
Australian Red Ensign

As above
Canadian Red Ensign

As above
New Zealand Red Ensign

As above
South African Red Ensign **

Royal Mail Ships (?)
Royal Mail Ensign

Royal Fleet Auxiliary vessels / Q-ships / Hospital Ships (?)
Admiralty, Government
Service or Transport Ensign

Troop Transports (?) / Hospital Ships (?)
Board of Trade Ensign

Vessels commissioned in one of the Commonwealth navies (ilcuding some landing ships), except Q-ships
White Ensign

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Notes

* The Red Ensign (undefaced) was also the civil ensign flown aboard merchant vessels registered in British India. While the Raj had its own version of the Red Ensign defaced with the so called "star of India", this flag had only a limited use:



Source: Flags of the World



Source: Wikipedia (see link above)

** Since 1928 South Africa had its own national flag, nonetheless...



source: Wikipedia (see link above)







Source: Flags of the World

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That should be all for now guys. In case you find any wrong information, if you think I have missed some notable flag or vessel type, or if you can provide new information relevant to the subject of this post, I will gladly update it with your imputs

Thanks for your hard work, gap!
By the way, American pilots who joined the British Air Force also fought under the British flag in the Battle of the English Channel. They were seconded to the British forces. This applied not only to airplanes but also to ships.