Arguably the first notable codebreaking during the American Revolution was conducted a few months after General Washington became Commander-in-Chief of the Continental Army.
The Revolutionary War began at Lexington and Concord when, in April 1775, the British troops despatched by General Gage from Boston clashed with local Americans. In May, a small party of Americans seized a fort of Ticonderoga by a surprise attack. In June, the patriots, though repulsed by the British army from a position near Bunker Hill, inflicted a heavy loss on the enemy.
Just as the Battle of Bunker Hill was fought near Boston, Continental Congress in Philadelphia appointed George Washington as Commander-in-Chief of the Continental Army. In July, Washington took over the command of the 16,000 patriots besieging Boston.
It was at the end of September that Nathaniel Greene, Brigadier-General from Rhode Island, brought before the Commander-in-Chief a man named Godfrey Wainwood [or Wenwood], who had a suspicious cipher letter.
Early in August, Wainwood, a baker of Newport, Rhode Island, was visited by a woman he knew in Boston, who wanted to see Captain James Wallace of Rose, Charles Dudley (the Royal Collector), or George Rome (a rich tory merchant). Wainwood found out that the woman wanted to deliver a letter addressed to "Major [Maurice] Cane in Boston on his majisty's service" and persuaded her to entrust the letter to him. His friend Maxwell, a schoolmaster, whom he consulted, opened the letter but only found that it was written in strange characters.
Wainwood just forgot about the letter but, after several weeks, he received a letter from the woman, complaining that "you never Sent wot you promest to send".
Actually, there was little suspicious in the cipher itself. It was not uncommon for private letters to be written in cipher. At the time, an envelope had not yet come into use and a letter was just folded and sealed with wax. It was suspicious, however, that a letter addressed to Boston was forwarded via Newport, Rhode Island, when it was written in Cambridge, just across the Charles River from Boston. And now, the letter from the woman shows that she found out, undoubtedly from some British contact, that the letter was not delivered. This made Wainwood and Maxwell report the letter to Henry Ward, Secretary of Rhode Island.
Thus, Wainwood came before Washington at the end of September. That evening, the woman was brought to the Headquarters in Cambridge. At first, she refused to tell the writer's name but threat and persuasion wore her out. She said the writer was Dr. Benjamin Church, her lover.
This must have been a shock to Washington. Church was a prominent physician in Boston and a member of the provincial congress of Massachusetts. It was Church, as chairman of the Massachusetts Committee of Safety, that signed on 3 May the commission (Grace Greylock Niles, The Hoosac Valley) to Benedict Arnold to lead a detachment to attack Ticonderoga. On 16 May, Church was entrusted (Journal of the Continental Congress) by the Masscachusetts Provincial Congress with a mission to go to Philadelphia to persuade the Continental Congress, as civil powers over the military, to take direction of the troops gathering around Boston. When Washington was appointed Commander-in-Chief of the Continental Army, Church was one of those who met him in Springfield and escorted him to Cambridge. Trust reposed in him was such that he was appointed as director of the hospital (Journals of the Continental Congress) that Congress had recently resolved to establish for the Continental Army..
Church was brought to the Headquarters in a few hours. He readily admitted that he wrote the letter but he said it was intended for his brother Fleming [actually, brother-in-law John Fleeming (Walker p.102)] in Boston. He said there was nothing criminal written in the letter but refused to decipher it.
The cipher letter was tackled by amateur codebreakers. One was Reverend Samuel West, who was a Harvard classmate of Church and was "credited with some knack of cryptography" (Weber, Freeman). When Washington's need was known, Elbridge Gerry, a man of 31 and later vice-president under James Madison, volunteered with Colonel Elisha Porter of the Massachusetts militia. (Kahn)
Washington received the deciphered text from them and found the two solutions identical. The letter (see below for the full text) told of Church's visit to Philadelphia, the strength of the continental army, projected invasion of Canada by the middle colonies, etc. It advised "speedy accommodation" with the colonists but demanded strict secrecy. It ended with a remark, "Make use of every precaution or I perish."
Washington reported the case to a council of generals on 3 October. Next day, Church was brought before the council and was confronted with the deciphered text. He admitted that the decipherment was correct but asserted that he intentionally exaggerated the strength of the Continental Army in the hope that the British might desist from attacking when the Continental Army was in want of ammunition.
The council's unanimous verdict was that Church was guilty of traitorous communications with the enemy. However, they felt the regulations adopted by Congress in June did not have appropriate stipulations for such a case. Thus, on 5 October, Washington referred the case to the Continental Congress and commented on possible deficiency of the regulations. (In the same month, Gage sailed for England and the command of the British Army in America was taken over by William Howe.)
On 7 November, Continental Congress decided to put Church in confinement in Connecticut (Journals of the Continental Congress). When Church pleaded for health problems, confinement was somewhat relaxed in January (Journals of the Continental Congress) and he was put on parole in May 1776 (Journals of the Continental Congress).
Some time after his release, he sailed for the West Indies but the vessel he was onboard was never heard from again.
For more than a century, there was little more than the ciphered letter that was held against Church, except for a reminiscence of Paul Revere written more than twenty years after the event. Church's guilt, however, has been accepted as definite since Allen French, General Gage's Informers (1932), revealed letters, in several hands, that proved to be from Church to Gage found in the Thomas Gage Papers at the Clements Library (Dirst et al.).
On 18 April, the day before the Revolutionary War broke out in Lexington and Concord, Paul Revere rode out of Boston to alert colonists including John Hancock and Samuel Adams. In April or May, his wife, Rachel, entrusted with Church a letter and 125 pounds of cash for her husband but Church delivered the letter to Gage and, presumably, kept the money (Clements Library).
When given a mission to go to Philadelphia, Church wrote, in his letter of 24 May 1775 to Gage, that should hostilities be long continued, people might seek independence and that a sudden attack would not be made by the troops gathering around Boston because they were sensible of the impracticability of conducting a war without assumption of the powers of government and they had to consult the Continental Congress. He wrote further, "I am appointed to my vexation to carry the dispatches to Philadelphia, & must set out tomorrow which will prevent my writing for some time, unless an opportunity should be found thence by water." and that Americans would not lay down their arms unless the intolerable Acts were all repealed by the British government. (Walker).
Some time after returning from Philadelphia, he received a letter from his brother-in-law, John Fleeming in Boston. The letter was in cipher and was concluded with a remark "If you cannot pass the lines, you may come in Capt. Wallice, via Rhode Island, and if you do not come immediately, write me in this character [i.e., in cipher], and direct your letter to Major Cane, on his Majesty's service, and deliver it to Capt. Wallace, and it will come safe". (Collections of the Massachusetts Historical Society, 1st series, Vol. VI (1806) quoted in Walker)
The letter that incriminated Church was written on 22 July in reply to this.
The cipher used in Church's letter was a simple monoalphabetic substitution cipher, in which each character represents one letter of the alphabet as shown below.
This section illustrates how such a cipher could be broken. The image below shows the three pages of the cipher letter in substitute characters. (The image of the manuscript cipher letter can be seen at George Washington Papers.)
Of the nearly 4000 characters, the "p"-like character is by far the most frequently used, occurring more than 500 times. This is considered to represent "e" in the plaintext. (In English, "e" is the most frequently used letter of the alphabet.) The characters "5", "v", "L", "9", "X", "theta", "reversed-R", "A" are the next most frequently occurring characters in this order. As it turns out, these correspond to the plaintext letters "t", "o", "i", "a", "n", "r", "s", "h". These nine letters correspond to the most frequently occurring letters in English "ETAONRISH".
For the time, it is conjectured that the "p"-like character may represent "e" in plaintext. Then, it is observed that a sequence like "5Ap" appears very frequently. This may correspond to "the", which is the most frequently used word in English. This conjecture is consistent with the earlier observation that "5" and "A" may be among the plaintext letters "TAONRISH".
In the following, the identification of these three letters have been applied to the first page (shown in blue).
Examining this (see esp. the highlight), one would note conspicuous patterns such as "th*ee" and "the*****ttee". These remind of words "three" and "the committee". The latter conjecture is supported by the double letter corresponding to "mm". Thus, the letters "r", "c", "o", "m", and "i" are now identified.
Now, one finding would lead to another. For example, one would find sequences which may be "attempts" and "attempting". The letters conjectured by these identifications, "a", "p", "s", "n", "g" are consistent with readings such as "his", "12 pieces", "280 pieces", "occasion", and "assistance", which is characteristic of three occurrences of "s". One would further notes words "received" or "receives", of which the latter is exlucded because the letter "s" is already identified. This reveals "v". These findings would faily reveal the plaintext.
Now, the beginning of the letter reads "I hope this *i** reach *o*". From the context (and the double letters in *i** gives a clue), it is not very hard to guess this reads "I hope this will reach you." This will identify "w", "l", "y", and "u", which leads to reading of "without success". The next phrase "ine**ectingthelast" would be "in effecting the last".
Now, it is as good as deciphered. There would be little doubt that the "W"-like character reads "b", numbers are numbers themselves, the "three-bar" symbol represents "&", and "=" is simply a double-hyphen, indicating that a word continues to the next line. Characters like "K", "J", "Z", "x", and "q" represent "k", "j", "z", "x", and "q". The person who prepared the cipher did not bother to think of symbols representing these low-occurrence letters!