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United Kingdom: Flags on the HMS Invincible in WW1

A question was asked about what flags would have been flown by the Royal Navy battle-cruiser HMS Invincible in WW1

The flag/ensign flown in addition to the White Ensign was either a Red Ensign, or a Union Jack. It was one or the other, at different times. At first the additional ensign was Blue (Grand Fleet Order No. 122 of 2 September 1914), but four days later was changed to a Union Jack (Grand Fleet Order No. 142), and confirmed by Interim Order No. 62 of 14 September 1914 (C.M.O. 45/1914).
“In view of the dangerous similarity between the White Ensign and the German Naval Ensign the following is to be carried our during the present War. All H.M. ships and vessels when at sea are to fly, in addition to the White Ensign at the Ensign Staff or its equivalent, at least one Union Flag in a conspicuous position on or near the foremast or only mast, using stays, rigging, or other projections which may be convenient.”

16 November 1914 the Admiralty cancelled C.M.O. 45/1914 and reissued the order verbatim, except that Red Ensign was substituted for Union Flag. (Interim Order S. 55). This was re-issued as Admiralty Interim Order S. 266/1915.
“In view of the dangerous similarity between the White Ensign and the German Naval Ensign the following is to be carried our during the present War. All H.M. ships and vessels when at sea are to fly a Red Ensign in addition to the White Ensign.”

On 11 January 1916 Admiralty cancelled S.266/1915 by the issue of Admiralty Interim Order S. 13/1916. In lieu of "All H.M. ships and vessels when at sea are to fly a Red Ensign in addition to the White Ensign", the following was substituted:
"On sighting a Man of War, or when in action, a Union Flag, in addition to the White Ensign is to be worn.

David Prothero, 23 February 2016