Book Codes between Benedict Arnold and John André (1779-1780)

Benedict Arnold is notorious for defecting to the British side during the Revolutionary War after his failed attempt to surrender West Point, a strategic point on the Hudson. The present article describes several book codes used by the conspirators. In addition to the well-known, typical book codes, an enciphered book code and other minor complications in their secret writing are described.

Table of Contents:

Arrangement for Secret Correspondence (May 1779)

Blackstone's Commentaries (May, June 1779)

Bailey's Dictionary (May - December 1779)

Enciphered Book Code and Other Additional Complications (December 1779)

Pocket Dictionary (May - August 1780)

Discovery (August - October 1780)


Arrangement for Secret Correspondence (May 1779)

When the Hudson valley was the focus of contest in 1777, Arnold distinguished himself as a patriot commander at the Battle of Saratoga. Arnold got injured in the leg during the battle and, when the British evacuated Philadelphia in June 1778, was placed in command of the city. By early May 1779, however, he decided to approach the British commander, Sir Henry Clinton, headquartered in New York.

Joseph Stansbury, a Tory merchant in Philadelphia, went to New York and, apparently with the help of Rev. Jonathan Odell (Van Doren, p.198), had a meeting with John André, who was Clinton's aid as well as close friend and handled the commander's secret correspondence with secret agents and informers (Van Doren, p.125; Willcox p.341).

After consulting with Clinton, André sent a letter to Stansbury dated 10 May 1779 (Clements Library), accepting the offer and telling the specific kinds of information wanted. Then, André went on to specify methods of secret communication:

André to Stansbury, 10 May 1779
.... You will leave me with a long book similar to yours. Three Numbers make a Word[;] the 1st is the Page[;] the 2d the Line[;] the third the Word[.] A comma is placed between each word[.] When only the first letter of the line is wanted in order to compose a Word not in the book, the number representing the Word will be 1 (Unit with a stroke across).
(Van Doren, Appendix No.1, p.200)

Representing a word with page, line, and word numbers is a typical method of a book code, as used by John Jay (see another article). The scheme for spelling appears to have been later revised to allow use of not only the first letter of the line but also any letter on the line. In the example below ("Sullivan"), the third letter with a stroke indicates a letter instead of the word at that position on the line.

André also proposed use of secret ink. A mark "F" or "A" would indicate that the letter should be processed by fire or acid to reveal the message hidden in an apparently innocuous message that might be written by Arnold's newly wedded young wife, Peggy, to her friend.

Thus began the treacherous correspondence between Arnold and André, which was conveyed by Stansbury in Philadelphia and Odell in New York. Odell even took on decoding and transcribing received letters (Van Doren, p.203, 443).

Blackstone's Commentaries (May, June 1779)

The book chosen for coding was William Blackstone, Commentaries on the Laws of England, 5th edition (cf. 7th edition (1775) at Google). However, with such a book, except for some common words such as "general" (35.12.8) or "men" (7.14.3), it was extremely difficult to find a word in the book. In one instance, Arnold had to look through to page 337 to find a word "militia". On the other hand, spelling a word not in the book was tedious. For example, "Sullivan" was enciphered as 35.3.1 35.3.2 34.2.4 35.2.5 35.3.5 35.7.7 35.2.3 35.5.2 (Kahn p.177, taken from Arnold to André, 18 June 1779).

In another example, "The confusion of town ...." is encoded as "7.1.3(the) 7.32.6(confusion) 7.1.1(of) 5.3.1 (t) 5.26.5 (own) ...", in which the line number "1" refers to the running head "§.1. of the Law ..." (If "7.1.3" is correct, "7.1.1" should be "7.1.2").

(In Van Doren's Appendix, the only despatches identified as coded with Blackstone are No. 6 (Stansbury to Odell, 26 May 1779 (Clinton Papers, vol.59:7)) and No.15 (Arnold to André, 18 June 1779 (Clinton Papers, vol.61:13)).)

Bailey's Dictionary (May - December 1779)

Arnold found he could write with dispatch by using a dictionary, in particular, a best-selling Universal Etymological English Dictionary by Nathan Bailey, 21st edition.

With a dictionary, it was straightforward to locate a desired word, though cryptologically it meant a weaker, one-part code. Now, the three-letter combination included the page, the column (1 or 2), and the line. Arnold added 1 to each number for enhanced security.

Stansbury reported use of the dictionary in a code letter (Van Doren, p.441 does not identify it as Blackstone but merely "keyed probably to long book mentioned" in the above.).

Stansbury to André, [before 23 May 1779]
To write with dispatch G[eneral] A[rnold] has made use of Bailys Dictionary 21st ed. 8to: London (1770) by R Ware &c. This I have paged for him beginning at A an abbre. &c. Each side is numbered and contains 927 pages. He adds 1 to each number of the page of the column and of the Line, the first word of which is always used to[o]. Zoroaster will be 928.2.2. and not 927.1.1. Tide is 838.3.2. and not 837.2.1. When he would express a number so (11,000). He depends on me for Convey[ing]. which is dangerous....
(Van Doren, Appendix No.4)

The first letter of Arnold to André, dated 21 May 1779, was forwarded by Stansbury between lines of an ostensible letter and reached Odell on 31 May 1779 but the latter heated it with fire only to find that it was too blotted to be legible. Odell asked Stansbury to send it again on 3 June but Stansbury said on 9 June he had lost the original but it was not necessary anyway because he had written several letters on a similar subject (Van Doren, p.202; Appendix No.7, 9, 11, 10).

Indeed, Arnold also wrote on 23 May to André (Van Doren, Appendix No.5) using Bailey's Dictionary.

It appears Odell could not understand part of a letter (now lost) encoded with Blackstone. Stansbury gave an explanation and repeated that Arnold used Bailey's Dictionary in his two despatches to André. In the following, the second paragraph was coded with Blackstone's Commentary.

Stansbury to Odell, 26 May 1779
I beg leave to recommend to your Perusal Blackstones Commentaries Page 46. of the 5th Edition Oxford the first Volume will solve the Question.
The confusion of a Town-meeting hath banished me to Morre'stown [represented by a codeword "Gravells"] for preservation ["61.22.1" does not fit the above Google edition, in which "preservation" should be "62.4.1" possibly due to this being a different edition]. In two letters for the Capt. [André, who is mentioned as "Captn André" in Odell's footnote to a letter of 4 June (Van Doren, p.444) etc.] Bayly's Dictiony 25th Lond: Edit: 8to is used, pageing it right. A, an abbreviation. (The body of the dictionary begins with "A. AN Abbreviature of Anno ....") An integer is added to the page, column, and line, i.e., word ["60.4.6" but "word" is the 6th word on line 20 in the above Google edition] (Because of Odell's failure to understand the scheme at this time, the emphasis in his decoding "and that is the word" is misleading. Here, "word" is merely an equivalent to "line.").
Paliwoledash (pseudonym)
[Odell's note] Integer, I presume, means only a single figure, as in no case can there be requisite a number larger than 9 to denote the word in a line of a Dictionary Column.
(Van Doren, Appendix No.6; p.204; Clinton Papers vol.:59:7)

As seen in this quotation, there were tumults in Philadelphia at a Town Meeting on 25 May 1779 and Stansbury had thought it wise to remove to Moorestown, New Jersey, where new arrangements were proposed for relaying letters (Van Doren, p.203, Appendix No.8)

In acknowledging the 26 May letter on 9 June, Odell asked Stansbury to "stick to your Oxford Interpreter", that is, Blackstone. (Van Doren, Appendix No.9, p.204) This crossed Stansbury's letter of the same date, in which the latter reiterated his preference of Bailey's Dictionary. (These exchanges were couched in terms as if they were talking about commerce or matters of personal interest.)

Stansbury to Odell, 9 June 1779
I asked your opinion lately on a passage in Blackstone's commentaries, whether you perfectly understood me I know not, but should be glad to have you joined me in opinion that my critique on that celebrated Author was at least defensible. I want to have a Baily's Dictionary -- having left mine in the hurry-scurry of moving last winter twelvemonth. If it is the same edition with yours it will be more to my satisfaction.
(Van Doren, Appendix No.10)


Somehow, some copies of the 21st edition of Bailey are dated 1775 (which Van Doren adopted in his annotation in Appendix No.5), while some copies are dated 1770 (as mentioned by Stansbury in Appendix No.4). From the location of the words ZOROASTER and TIDE (given as examples by Stansbury (see above)), these copies seem to be identical.

Since the book was not paginated, Stansbury manually paged it for Arnold (Van Doren, Appendix No.4; the page number of the digital copy at Internet Archive minus 20 gives the page number for these pages but minus 15 for the first pages. There seem to be some missing pages in the pdf.).

Internet Archive (1775)

Google (1775)

HathiTrust (1775)

HathiTrust (1770)

The year "1770" seems to be the correct date because the 23rd edition came out in 1773. The "25th" mentioned in Stansbury to Odell, 26 May 1779 (see above) must be an error because the dictionary was yet the 24th edition as of 1782 (HathiTrust). When he wrote it, Stansbury, having hastily moved to Moorestown, had left his book in Philadelphia.

Examples in this code are "582.3.30(our) 348.2.66(friend) S[tansbury] ...." "738.2.5(Seizing) 589.3.28(paper[s]) is 422.3.31(impossible) ...." (The page, column, line numbers are augmented by 1.) (Van Doren, Appendix No.5, Clinton Papers, vol.59:1)

23rd Edition

When Stansbury acquired Bailey's Dictionary, it was the 23rd edition (1773) (Google, HathiTrust; the page number can be obtained by subtracting 23 from the numbering of the downloaded pdf from Google but the offset varies possibly due to missing pages (e.g., after p.650 and p.802 of pdf) in the pdf). He used it in his letter to André dated 11 July 1779 (Van Doren, Appendix No.16; he also used it in Appendix No.22) and explained to Odell that it was "on the 23d principle (sans integer)". (The remark "sans integer" (without integer) means Stansbury did not add 1 to the numbers, as Arnold did.) Odell had to obtain a copy through Stansbury at 60 Continental dollars. Realizing that it was different from the edition (presumably the 21st) used between André and Arnold, Odell sent his copy to André but asked it be returned (Van Doren, Appendix No.17, 19; p.211).

André wrote directly to Arnold at the end of July but Stansbury conveyed Arnold's disappointment, encoded with Bailey's Dictionary, 23rd edition (Van Doren, Appendix No.22). After this, the conspirators barely maintained occasional exchanges with no progress in negotiation (Van Doren, p.219, 243). The first phase of the contact was now over.

Enciphered Book Code and Other Additional Complications (December 1779)

The letter from Stansbury to Odell, 3 December 1779, still used Bailey's 23rd edition (note attached to Clinton Papers, vol.78:40) but employed additional complications. It is a "mixture of code, cipher, French, and English" (Van Doren, Appendix No.26)

Use of the 23rd edition is confirmed with an example of 180.1.18 (Congress) (no numbers added).

Moreover, this letter employs code groups of a different type: bf51d (arrived, p.58), mfy18 (Congress, p.180), bbb16 (office, p.555), etc. The present author found that the letter prefix enciphers the page of Bailey's 23rd edition according to the following substitution. (The column/line indication scheme is not clear.)

Not only the headwords of the dictionary but also phrases are used in encoding. The code group "ndc57,18+19+20" encodes "as soon as", which are the 18th, 19th, and 20th words of the entry EMBRYO on p.276 (again, the column/line indication "57" is not clear).

In addition, place and personal names ("Sullivan", "Gates", "Baltimore", "Chesapeak[e]", "Hartford", etc.) are enciphered according to the following substitution. That is, "6" represents D but "6" with an overdot represents M and "6" with two dots above represents V. By coincidence, this is similar to the Roe-Conway Cipher used in the 1620s (see another article)

While many figures are written in the clear, some figures as well as some small words are written in French: "quarantequatrepourun" (forty four for one), "pendant le fdm29" (during the war).

Pocket Dictionary (May - August 1780)

In late May 1780, Arnold discreetly conveyed to Washington through his friend General Schuyler that he wanted a command of the Highlands and West Point, though his wounds in the leg still made it very painful to walk or ride (Van Doren, p.258-259).

About this time, Arnold renewed his offers by sending a person, probably Stansbury, to New York. The British Commander-in-Chief Clinton was absent in besieging Charleston, South Carolina, since December (Wikipedia), and Hessian General Knyphausen was in command in New York, with Beckwith instead of André. It was arranged that a pocket dictionary was to be used for encoding (Van Doren, p.260-261, Appendix No.29).

From the code numbers occurring in the letters, the dictionary had about 300 pages ("absolutely" on p.2, "your" on p.287). Although the dictionary has not been identified, examples of dictionaries with similar size are: A new English-Welsh dictionary (1812, the body is about 340 pp.) (Internet Archive) and Entick's New Spelling Dictionary (1812, the body is about 360 pp.) (Internet Archive) (an edition of Entick was also used by John Jay).

The pocket dictionary was used as early as 7 June 1780, when Arnold disclosed a proclamation of which he was entrusted by Washington to secretly print a number of copies (Van Doren, Appendix No.30, 31, p.263 ff.). At the same time, Arnold requested a conference with a British officer. In early July, Arnold felt sure he would get the command of West Point (Van Doren, p.269, 273, Appendix No.36, 38) but still no answer was given to his request. Beginning to be suspicious, he wrote on 11 July to André in disguised handwriting, using commercial terms, and again on 12 July, this time using the dictionary code. These letters were delivered together by a trusted messenger (Van Doren, Appendix No.37, 38, p.272-273). The next day, a reply to the June letters was received but, finding it unsatisfactory, Arnold sent another letter encoded with the same book code on 15 July via Stansbury, stating his demands and informing that he would set off for West Point on the 20th, though the appointment was not yet finalized (Van Doren, Appendix No.39, 40, p.274-275). After receiving another frustrating reply, sent the day before Stansbury's messenger reached New York, to a previous letter of 7 July, Arnold rejoined the army on the Hudson at the end of July (Van Doren, Appendix No.41, p.277, 276, 283). Arnold sent information to his wife Peggy in Philadelphia, expecting it to be forwarded to New York by Stansbury (Van Doren, Appendix No.46, 47, 48, 49, p.280-281). At the time, Clinton was considering an attack on New Port, Rhode Island, which served as a base for the French fleet and Arnold conveyed information of Washington's movement. (Clinton later assessed that the intelligence (e.g., 12 July) that the French fleet was coming to Rhode Island might have been of the greatest benefit to the British had it not been for Admiral Arbuthnot's delays (Van Doren, p.362).)

In the meantime, a reply of 24 July, accepting Arnold's demand (except for preliminary indemnification regardless of performance) and also intimating that André himself was willing to meet him in person, reached Stansbury in Philadelphia only on 8 August and had to be detained in Peggy Arnold's hands for some days because a trustworthy carrier could not be found. It did not reach Arnold until 24 August (Van Doren, Appendix No.42, 43, p.277-281). André's reply was signed "297.8.15 244.9.34", which stands for Y-- S--, if the same dictionary was used (cf. 294.9.18 (your), 240.8.13 (since), 243.8.23 (sincerity), with each number augmented by 7).

The last known use of this dictionary code was Arnold's letter of 15 September (Van Doren, Appendix No.58).

Arnold to André, 12 July 1780 (Van Doren, Appendix No.38)

This and the next section give examples of letters encoded with the pocket dictionary. (They are different from other published transcriptions but I do not claim they are more accurate transcriptions because I have more or less liberally edited these so as to be cryptologically more consistent. For example, "1" has been replaced with 2, which look similar to "1" in the manuscript.)

Arnold enhanced security of the dictionary code by adding 7 to each number (hence, the second number was always 8 or 9) but he did not apply it to the line number in this letter (cf. the postscript of Arnold's letter of 15 July about his letter of the 13th, which may be an error for the 12th; Van Doren, Appendix No.40, p.274).

I 293.9.7(wrote) to C_t. B.(Beckwith) 183.8.2(on) the 7th 152.9.17(June) that a F__(French) 112.9.17(fleet) and 22.8.29(army) were 105.9.5d(expected) to 11.9.4(act) in 62.8.20(conjunction) with 263.8.19(the) A(American) 22.8.19(army)[.] the 230.8.13(same) 263.8.17(time) I gave Mr. S---y(Stansbury) a 164.8.16(manifesto) 147.8.24d(intended) to be 209.9.21d(published) in C----a(Canada) and have from 263.8.17(time) to 263.8.17(time) 58.8.27(communicated) to him Such 147.8.21(intelligence) as I 264.9.5(thought) 147.9.16(interesting), which he 24.9.12s(assures) me has 269.9.23'd(transmitted) to you[.] I 129.8.7(have) 216.9.22'd(received) no 19.8.29(answer) to 175.9.17(my) 158.8.8(letter) - or any 277.8.23(verbal) 168.9.13(message) ------- I 105.9.5(expect) soon to 57.9.7.(command) at 288.9.8(West) 198.9.26→198.9.24,(Point) and most --- 291.8.27(wish) an 149.8.27(interview) with --- 255.9.11.(some) 148.8.22(intelligent) 182.8.28(officer) in whom a 175.9.12(mutual) 61.8.28(confidence) could be 196.9.16(placed) --- the 177.8.8(necessity) is 103.8.19(evident) to 22.9.3(arrange) and to 66.8.15(cooperate) -- An 182.8.28(officer) 169.8.25(might) be 260.8.5(taken) 205.9.3(prisoner) near that 200.9.18(post) --- and 192.9.9'd(permitted) to 224.9.9(return) on 188.8.13(parole) or some ---- 182.8.28(officer) on 188.8.13(parole) sent 185.6.24(out) to 95.9.12(effect) an 104.8.1(exchange)[.]
120.9.7(General) W----(Washington) 105.9.5's(expects) on the 22.9.14(arrival)---- of 263.8.19(the) F----(French) 272.8.7s(Troops) to 56.9.8(collect) |30.000| 272.8.7s(troops) to 11.9.4(act) in 62.8.20.(conjunction)[.] If 179.8.25(not) 84.8.9'd(disappointed), 177.9.28(New) Y----(York) is 111.9.27'd(fixed) on 23.8.10(as) the 111.9.13(first) 180.9.19(object)[;] if his 180.8.21(numbers) are 179.8.25(not) 255.8.17(sufficient) for that 180.9.19(object) 44.8.9(can)_a_(Canada) is the 234.8.14(second)[,] of 289.8.17(which) I --- 44.8.9(can) 145.8.17(inform) 294.9.12(you) in 266.8.17(time) as well as [of] 103.8.11(every) 184.9.15(other)---- 80.9.20(design) ---- I 149.8.7(have) 10.8.22'd(accepted) the 57.9.7(command) at 288.9.9(West) 198.9.26(Point) as a 100.9.18(post) in 289.8.17(which) I can 221.8.6(render) the 173.8.19(most) 102.8.26(essential) 236.8.21's(services)--- and 289.8.17(which) will be in 175.9.17(my) 87.8.7(disposal)--- the 166.8.11(mass) of the 191.9.16(people) are 129.19.21'y(heartily) --- 266.9.14(tired) of the 286.8.20(war) and 291.8.27(wish) to be on --163.9.4(their) 115.8.16(former) -'r 114.8.25ing(footing) --- 263.9.14(they) are 207.8.17ed(promised) 125.8.15(great) 103.8.60(events)--- from this 294.8.50's(year's) 104.9.26(exertion) -- If 84.8.9ed(disappointed) -- 294.9.12(you) 129.8.7(have) only to 193.8.3(persevere) and the 64.9.5(contest) 290.9.20(will) 245.8.3(soon) be at an 99.8.14(end). the 204.8.2(present) 253.8.7s(struggles) are 159.8.10(like) the 187.8.11(pangs) of a 94.9.9ing(dying) 164.8.24(man)[,] 279.8.16(violent) but of a 238.8.25(short) 93.9.28(duration).
(Page 2)
As 158.9.25(life) and 115.9.12(fortune) are 226.9.3'd(risked) by 236.8.20ing(serving) 131.9.27(His) 163.9.6(Majesty) -- it is 177.8.6(necessary) that the 156.8.11'r(latter) 236.9.28.(shall) be 234.9.3ed(secured) as well as the 98.8.22s(emoluments) I 121.9.25(give) up, and a 59.8.5(compensation) for 236.8.21's(services) 14[.]9.27(agreed) on, and a 255.9.11.(sum)-- 13.8.6'd(advanced) for that 211.8.14(purpose) -- which I have 168.8.20ed(mentioned) in a 158.8.8(letter) 289.8.17(which) 10.9.9.(accompanies) this, 289.8.17(which) Sir 300.8.4(Henry) 290.9.20(will) 7 not, I 31.9.13(believe), think 282.9.12(unreasonable)
152.9.12(July) 12th. 80--
I am Sir
Your Humble Servt
Mr. Jno Anderson
J. 172.9.12(Moore)----

P.S. I have 125.8.15(great) 61.8.28(confidence) in the 30.8.8er(Bearer) but 30.8.8.(beg) S.(Sir) 300.8.4(Henry) will 264.9.26(threaten) him with 131.9.27(his) 223.8.1(resentment) in 46.8.19(case) He 10.8.9's(abuses) the 61.8.28(confidence) 196.9.16(placed) in him 289.8.17(which) 290.9.20(will) 39.9.24(bring) 48.8.19(certain) 228.8.23(ruin) 183.8.2.(on) me. The 30.8.8'er(bearer) 290.9.20.(will) 39.9.24(bring) me |200| 126.9.141s(Guineas) and 190.8.11(pay) the 220.8.50(remainder) to 45.8.10(Captn) A-----, who is 222.9.15ed(requested) to 216.9.22(receive) the 80.8.8(deposit) for Mr. 172.9.12(Moore)

Arnold to André, 15 July 1780 (Van Doren, Appendix No.40)

Inclosed in a cover addressed to M. Anderson [André]
274.9.19(Two) 75.8.17s(days) 240.8.13(since) I 216.9.29d(received) a 158.8.15(letter) without 74.9.32(date) or 239.9.13(signature), 145.8.24ing(informing) me that S[ir] 300.8.11(Henry) -- was 181.8.8(obliged) to me for the 148.8.28(intelligence) 58.8.34(communicated), and that he 196.9.23(placed) a 117.9.35(full) 61.8.35(confidence) in the 243.8.23(sincerity) of my 148.8.37(intentions), etc. etc. etc. ---- On the 264.8.22(13th) 147.9.22(Instant) I 12.8.16ed(addressed) a 158.8.15(letter) to you expressing my 235.9.19s(Sentiments) and 105.9.14s(expectations), viz, that the 114.8.21(following) 203.8.28(Preliminaries) be 236.9.8d(settled) previous to 66.8.22ing(cooperating). First, that S[ir] 300.8.11(Henry) -- 234.9.9(secure) 266.9.34(to) me my 207.9.24(property), 275.9.14(valued) at 262.8.14(ten) 264.9.19(thousand) 201.8.32(pounds) 250.9.22(Sterling) to be 190.8.18d(paid) to me or my 130.82.29s(Heirs) in case of 161.8.35(Loss); and, as soon as that shall 128.8.24(happen), ---- 134.9.19(hundred) 201.8.32s(pounds) 250.9.22(Sterling) per 19.8.24(annum) to be 234.9.10d(secured) to me for 158.9.32(life), in 158.9.29(lieu) of the 190.8.18(pay) and 98.8.29s(emoluments) I 121.9.32(give) up, for my 236.8.25(Services) as they shall 80.9.13(deserve) ---- If I 198.9.34(point) 185.8.31(out) a 197.8.8(plan) of 66.8.22n(cooperation) by which S[ir] 300.8.11(Henry) ---- 236.9.35(shall) 200.9.19(possess) 131.9.34(him) 235.8.14(self) of 288.9.16(West) 198.9.33(Point), the 120.8.17(Garrison), etc. etc. etc. 274.8.25(twenty) 264.9.19(thousand) 201.8.32s(pounds) 250.9.23(Sterling) I think will be a cheap purchase for an 180.9.25(object) of so 174.8.8(much) 139.8.33(importance). At the same time I 222.9.22(request) a 264.9.19(thousand) 201.8.32s(pounds) to bee 190.8.18'd(paid) my 14.9.18(Agent) ---- I 105.9.12(expect) a 117.9.36(full) and 106.8.12(explicit) 19.8.37(answer) -- The 274.8.24(20th) I 236.8.36(set) of[f] 114.9.11(for) 288.9.16(West) 198.9.35(Point) -- [A] 193.8.16(personal) 149.8.33(interview) with an 182.8.35(officer) that you can 61.8.34(confide) in is 9.9.24(absolutely) 177.8.12(necessary) to 197.8.8(plan) 166.9.20(matters). 148.9.28(In the mean time) I 236.9.36(shall) 58.8.34(communicate) to 185.6.30(our) 175.9.19(mutual) 117.8.9(Friend) S______y [Stansbury] 15.9.33(all) the 148.9.28(intelligence) in my 201.9.9(power) 283.8.11(until) I have the pleasure of 294.9.18(your) 19.8.36(answer).
152.9.19(July) 119.9.26(15th) [1780]
172.9.19(Moore [Arnold])
To the 159.9.11(line) of my 158.8.14(letter) of the 264.8.12(13th) 147.9.22(instant) I did not add 236.9.12(seven)

Partial Reconstruction of the Pocket Dictionary

The image below is a partial reconstruction of the pocket dictionary of code numbers (page.column.line) used in Arnold's above letters of 12 and 15 July 1780. The offset of 7 has been removed from the numbers in this table. The at sign (@) indicates numbers used in the 15 July letter (the other, unmarked entries had no offset in the line number). Some code groups are based on numbers corrected on the basis of consistency rather than images of the manuscript. I tried not to be too aggressive in the correction so there still remain some inconsistencies.

Anyone who has identified the dictionary from this table is kindly asked to contact the present author.

Stansbury to Odell, 25 August 1780

The extant short extract of Stansbury's letter to Odell on 25 August 1780 (Van Doren, Appendix No.50) also appears to employ the same pocket dictionary but column indication is made more diverse. The following shows at least the page numbers (and more or less line numbers) match those of Arnold's letters above.

@ indicates a line number augmented by 7.

In addition, the simplest Caesar cipher is used to obscure acronyms: TJD for SHC (Sir Henry Clinton), HX for GW (George Washington), OZ for NY (New York), and TD for SC (South Carolina).

Discovery (August - October 1780)

On 3 August, Arnold was given a command of West Point by his request, despite his assignment to the left wing two days before. (Van Doren, p. 283) He soon took residence at a house opposite West Point.

It was difficult to arrange a meeting with André, an enemy officer. An attempt on 11 September came to nothing (Van Doren, p.309-310).

When Arnold was confidentially asked by Washington on 15 September to provide a guard when the commander-in-chief would cross the Hudson to meet the French General Rochambeau at Hartford, Connecticut, he immediately informed the British of the plan in a depatch encoded with the pocket dictionary (Van Doren, Appendix No.58, p.314).

André came up the Hudson on a British sloop Vulture and came on shore on some pretext and met Arnold in the forest on a moonless night of 21-22 September (Van Doren, p.332-333). In the morning, the Vulture received bombardment by Americans ignorant of Arnold's plans and had to leave her position. André had to travel by land (Van Doren, p.334). On the 23rd, André was stopped by American locals. Thinking they were loyalists, André did not produce Arnold's pass until too late, when papers given by Arnold hidden in stockings were found. He was taken to an American post. A report of the capture was sent to Arnold, still unsuspected, while a messenger was sent with the captured papers to Washington, who was to visit West Point on his way back from Hartford. (Van Doren, p.340-342).

On the 23rd, while Washington was late to arrive, Arnold was given the report of André's capture and hurried to his barge to seek refuge on the Vulture, leaving a message that he went over to West Point. Washington arrived and took breakfast and went over to West Point but returned without him. (Van Doren, p.345-346) When he read the papers that came in his absence, he sent after Arnold his aid Alexander Hamilton, who returned with a letter for Washington from Arnold, now safe on the Vulture, in which he justified his act (Van Doren, p.348).

André was kindly treated by Washington and other Americans and bore no grudge to Clinton or Arnold (Van Doren, p.363-364) but was sentenced death as a spy and was executed on 2 October.


William L. Clements Library

Henry Clinton Papers 1736-1850 ... Subject Index (pdf) ("Arnold, Benedict, alliance with British" on p.61; "Intelligence, letters and documents in cipher and code" on p.105)

"Spy Letters of the American Revolution"

    Terms of Betrayal (10 May 1779, John André to Joseph Stansbury) Letter

    Military Secrets (12 July 1780, Benedict Arnold to John André) Letter in Code, enlarged, decoded

    Selling West Point (15 July 1780, Benedict Arnold to John André), Letter in Code, enlarged, decoded

    The Death of John Andé (29 September 1780, John André to Henry Clinton) Letter


Van Doren (1941), Secret History of the American Revolution

William B. Willcox (1962, 1964), Portrait of a General

"Benedict Arnold", Wikipedia

"Arnold Cipher", Wikipedia

David Kahn (1967), The Codebreakers

Mark M. Boatner III, Encyclopedia of the American Revolution

©2016 S.Tomokiyo
First posted on 26 June 2016. Last modified on 26 June 2016.
Articles on Historical Cryptography
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