The story of Sir John Trevanion's escape from Colchester Castle is quoted by many authors (including myself) as an example of a spectacular use of a concealment cipher. However, its authenticity does not seem to be established.
The story goes like this.
At the time of the English Civil War, Sir John Trevanion was locked up in Colchester Castle in Essex (to the northeast of London). His fellow royalists Sir Charles Lucas and Sir George Lisle had just been executed and he was expecting the same fate. Then, the gaoler delivered him a letter. On the following evening, Sir John asked to be allowed to pass an hour of private devotion in the chapel. The request was granted but when the promised hour had expired, the prisoner was gone.
As it happened, the letter delivered at the last minute told Sir John a way to escape. The letter must have been examined so as not allow conveyance of such information but the message was cleverly hidden in apparently innocuous words from a friend consoling a doomed prisoner.
The letter is as follows:
Picking up each third letter after punctuation reveals the true message:
PANEL AT EAST END OF CHAPEL SLIDES.
An attempt to check this episode against historical facts would immediately bring up some doubts. First, Colchester fell in 1648 but one known John Trevanion (Wikipedia) had died in 1643. Some versions of the story mention execution of Charles Lucas (Wikipedia) and George Lisle but historical records do not mention a Trevanion with these prisoners. According to Penny cyclopaedia of the Society, Vol. IX (Google), p.32 and Wikipedia, "Siege of Colchester", the other persons sentenced to death with Lucas and Lisle were Bernard Gascoigne and Colonel Farre and the former, being a foreigner, was reprieved and the latter escaped.
No modern author seems to quote a primary source of this episode. The authority in the field, David Kahn's The Codebreakers cites C. C. Bombaugh, Oddities and Curiosities, ed. Martin Gardner (reprinted New York: Dover Publications, inc. 1957). According to the Introduction of the 1961 edition in the possession of the present author, the chapters reprinted are from the third and last revision (in 1890) of Gleanings for the Curious (1874), Bombaugh's most popular book.
Trevanion's cipher is mentioned by none of the major works on cryptography by earlier English authors: John Falconer's Cryptomenysis Patefacta (1685) (see another article), John Davys' An Essay on the Art of Decyphering (1737) (see another article), Philip Thicknesse, A treatise on the art of decyphering and of writing in cypher with an harmonic alphabet (1772) (cf. an article in Japanese), and William Blair's 'Cipher' in Rees' Cyclopaedia (1807) (see another article).
A quick search on the web reveals that the same story is repeated by many publications during 1860s to the early 20th century. The earliest that could be found dates back to 1853.
1853 (UK): The National miscellany: A magazine of general literature, Volume 1, London, p.356 (Google)
1863 (UK): Once A Week: Volume 9, London, p.610 (21 November 1863) (Google)
1863 (US): Harper's Weekly, 19 December 1863, New York (quoted below). This issue can be found online at an American Civil War website but I could not locate the source.
1864 (NZ): Otago Witness, 26 March 1864, New Zealand (Papers Past) This cites "Once a Week" (above) as the source.
1866 (US): Albert J. Myer, A manual of signals: for the use of signal officers in the field, and for military and naval students, military schools, etc., New York, p.311 (Google) This cites its source as Harper's Weekly, December 19, 1863.
1869 (UK): S. Baring Gould, M.A., Curiosities of Olden Times, p.15 (Internet Archive)
1874 (US): Gleanings for the Curious from the Harvest Fields of Literature (the basis of Kahn's quotation mentioned above) (Google (1875), Internet Archive (1890))
1908 (NZ): Star, 18 February 1908, New Zealand (PAPERSPAST)
1908 (NZ): New Zealand Tablet, 9 April 1908, New Zealand (PAPERSPAST)
1913 (US): The Century illustrated monthly magazine, Vol. 85 (Google, Internet Archive)
It seems all the versions other than the one of 1853 seems to be textually identical. The 1853 source includes some names not mentioned by later sources and may be worth quoting.
One known Bampfylde (Bampfield) (see another article) often carried secret letters to and from Charles I held in the Isle of Wight. About June-July 1648, Bampfield went to Holland but totallly lost his credit with the Duke of York, whom he helped escape from the Parliamentarians earlier this year. He returned to England in the latter part of 1648 but his connection with Colchester could not be confirmed. (Colonel Joseph Bampfield's Apology p.131, 129, Jock Haswell, James II p.39-40)
Some years ago, the present author found a snippet of a seemingly relevant article on the episode on Google Books, which cannot be viewed now. According to private notes at hand, it was from Journal of the British Archaeological Association vol.28 (1922). It said "Local legends speak of a prisoner escaping from the castle during the period of the civil wars by making use of a communication conveyed to him in a cypher letter. The message read, 'Panel at east end of chapel slides', and in a recess of a wall of the crypt was discovered the remains of a narrow stairway. The passage is blocked ...." The 1922 excavation is recorded here, referring to pp.198-208 of the above volume and other publications.
According to Gardiner, History of the Great Civil War, 1642-1649, p.199, n.1 (Internet Archive), there were many dubious "catchpenny productions" at the time, allegedly derived from escaped townsmen. While Trevanion's episode may be one of such stories, the cipher seems too elaborate to be a mere sham. A reader who could locate a more authentic source of Trevanion's episode is kindly asked to contact the present author.