Sir Henry Clinton's Hourglass Cipher

In the summer of 1777, Sir Henry Clinton remained in New York while Sir William Howe, Commander-in-Chief of the British army in America, went south to attack Philadelphia. Clinton was uneasy about his superior's move. This year, the British government planned a grandiose strategy for General Burgoyne to progress down the Hudson valley from Canada to effect a junction with the army in New York. By rallying loyalist residents on the way, the rebellious New England could be cut off from the rest of the colonies. But Howe's expedition to Philadelphia meant he could not cooperate with Burgoyne.

At first, Burgoyne's march went well and he took Fort Ticonderoga in early July. When Howe heard it in New York, he sent Burgoyne a message dated 17 July hidden in a quill (see Clements Library) to inform Burgoyne of his intention. On 23 July, he sailed for his cherished expedition for Philadelphia.

Left in New York, Clinton wrote criticism of his superior.

Sir W. Howe is gone to the Chesapeak bay with the greatest part of the army. I hear he is now landed but am not certain. I am left to command here with too small a force make any effectual diversion in your favour. I shall try something at any rate. I own to you I think Sr W's move just at this time the worst he could take. Much joy on your success.
Clinton to Burgoyne, 10 August 1777

This letter, which did not get through, was written with a kind of grille cipher. Upon first looking, the letter bears a completely different text from the above message. However, when a mask (grille) -- a sheet with a cutout shaped like an hourglass -- is applied, the true message is revealed.

The original letter can be seen at the website of Clements Library (cover letter without mask; true message with mask). The letter is also published in Thomas Fleming, Liberty! The American Revolution, p. 259.

In the meantime, Burgoyne's progress had started to slow down. After he took Fort Ticonderoga in early July, it took 21 days to reach Fort Edward on the upper Hudson, just 30 kilometers south of Ticonderoga. As of 6 August, he was still optimistic and wrote to Clinton at Fort Edward that he would be in Albany by the 23rd at the latest. In mid-August, however, his detachment was beaten at the Battle of Bennington. Burgoyne had made little progress from Fort Edward even in September.

At this juncture, Clinton offered to make a diversion.

You know my goodwill, & are not ignorant of my poverty. If you think 2,000 men can assist you effectually, I will make a push at Montgomery in about ten days. But ever jealous of my flanks; if they make a move in force on either of them, I must return to save this important post. I expect reinforcements every day. Let me know what you would wish.
Clinton to Burgoyne, 11 September 1777

This letter, again written with the hourglass grille, is published in Christopher Hibbert, Redcoats and Rebels, p.189.

Burgoyne barely repulsed the Americans under General Gates at the Battle of Freeman's Farm, near the village of Saratoga, on 13 September. It was when he was about to make a desperate attack on the Americans that the above letter of Clinton reached him. Burgoyne had lost the mask to read the message but, remembering the general shape of the cutout, he produced another sheet with a similar hole and could read Clinton's message. Burgoyne decided to wait for Clinton's diversion. However, Burgoyne's reply reached Clinton only on 29 September.

Upon receiving Burgoyne's reply, Clinton moved fast and took Fort Montgomery and Fort Clinton on the west bank of the Hudson on 6 October.

However, Burgoyne's situation was growing worse. A messenger (Captain Alexander Campbell), who had left Burgoyne's army on 28 September, arrived on 5 October just as Clinton was trying to draw the enemy's attention from the west side of the Hudson during his diversionary campaign. According to the messenger, Burgoyne's force was now reduced to 5000 and facing an enemy of double that number and Burgoyne wanted Clinton's "most explicit orders, either to attack the enemy in his front or to retreat across the Lakes".

Next day, Clinton sent the messenger back with his reply that he could not presume to give orders. On 8 October, after succeeding in taking the forts, Clinton wrote from Fort Montgomery in a cheerful tone: "Nous y voici, and nothing now between us but Gates. I sincerely hope this little success of ours may facilitate your operations." The letter was written on thin paper rolled up in a small silver bullet. (Silver was used to avoid lead poisoning for the messenger when he had to swallow it.)

On 9 October, another messenger (Captain Thomas Scott), who had left the northern army a day earlier than Campbell, brought a similar message to that of Campbell. Next day, Clinton sent the messenger back with a reply.

But neither Campbell nor Scott got through. Communications were now difficult and they had to return. Another messenger, Daniel Taylor, carrying the letter of 8 October in a silver bullet, was captured by the rebels. He swallowed the bullet before being searched but he had been seen. He was given a strong emetic, which took effect. He snatched the vomited ball and swallowed it again but it was discharged by another dose of emetic. He was tried as a spy and hanged.

Meanwhile, Burgoyne was defeated on 7 October at the Battle of Bemis Heights. Burgoyne learned from a scout in the morning of 16 October that Clinton took Fort Montgomery and that British naval vessels were above Kingston upon the Hudson. But he had already started negotiations with Gates and surrendered at Saratoga on 17 October 1777.

Shortly before Burgoyne's surrender, Howe defeated George Washington at the Battle of Brandywine and took Philadelphia. The occupation of the de facto American capital, however, held little importance compared to the strategic value of the Hudson valley. Howe resigned and Clinton, his successor as the Commander-in-Chief of the British army in America, abandoned Philadelphia next year.

©2009 S.Tomokiyo
First posted on 12 November 2009. Last modified on 1 January 2010.
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