The only intriguing thing about the letter is why The Times published it. They normally only print letters from people who are eminent in their field or have special experience. An officer who retired in the rank of Lieutenant from a service that promotes officers on time, rather than merit, to Lieutenant Commander seems unlikely to have met The Times's criteria.
Probably best to ignore the letter. Alternatively reply in equally outrageous vein - eg, the RAF destroyed more U-Boats than the RN in WW2, so perhaps HM warships ought to be sailing under the light blue ensign with roundel.
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presto digitate