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Spycraft: The Cardan Grille System

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One of the most exciting elements of the TURN premiere is the debut of 18th century spycraft in the form of a shiny copper grille used by Abraham Woodhull to decipher a secret message hidden within a British letter.  Not only is it a dramatic signal of Abraham’s decision to become involved in intelligence gathering — it’s also an authentic, documented method of spycraft used during the American Revolution!TURN01 - spycraft_4  TURN copper grille

 

 

 

 

 

This particular method of secret  message writing is known as the Cardan system, and the copper plate is a version of a Cardan (or Cardano) Grille, named after Girolamo Cardano (aka Jerome Cardan), who invented it in the 16th century. John Nagy, in his book Invisible Ink: Spycraft of the American Revolution, provides a handy description:

[A] Cardano Grille [was] a sheet of stiff material with irregularly spaced rectangular holes which was placed over the writing paper. The secret message was then written in the holes, the grille or mask removed from the writing paper, and a harmless message was filled in around the secret message to camouflage its being there. To read the message, an identical grille or mask was placed over the writing.(Invisible Ink, p3)

When executed successfully, the “dummy” or cover message would be unremarkable enough to avoid raising suspicion that a secret message was contained within it.  A letter authored by a British or Continental officer full of broken or awkward sentences would almost certainly be scrutinized for secret meanings if intercepted by the enemy.  Even then, it’d be nearly impossible to discern the secret message without possessing the matching grille, which makes the Cardan system a fairly secure one.  You need both pieces in order to decipher the real message.

TURN01 - spycraft_1The system was not without its weaknesses, however. The presence of the grille itself is almost guaranteed to arouse suspicion – as we see in the pilot episode when Abraham pulls the copper grille out of its envelope. Only after discovering the grille does he look around for something to match it with.  (For that matter, the grilles were usually stiff paper or cardboard, and not shiny copper sheets that would attract attention and be more difficult to conceal. Paper grilles are much easier to create, and can be folded or rolled up for easier transport.) Abraham was also pretty fortunate to have discovered the correct orientation of the grille on the first try – since there are four possible ways to position a rectangular grille like the one we saw in the show. There’s a slight chance that the reader might take away an incorrect message if they position the grille incorrectly.

Some people expand the definition of the “Cardan system” to include all shapes and forms of message masks, but Cardano’s original method used rectangular cutouts exclusively. Sir Henry Clinton — the British general who appointed John André as his Chief of Intelligence —  used numerous Cardan grilles and message masks in both personal and official correspondence, even as early as 1776.  Many of them still survive in the Clinton Papers which are housed at the University of Michigan’s Clements Library.  The contents of that collection strongly suggest that we’ll see other variations of “masked” messages in future episodes of TURN — so I won’t discuss those just yet.

The Cardan Grille is one of several 18th century methods of spycraft referenced in the TURN opening credits.
The Cardan Grille system is one of several 18th century methods of spycraft referenced in the TURN opening credits.

During the Revolutionary War, the Americans preferred other forms of cryptography (secret writing) over grilles and masks. The Cardan Grille system is more accurately described as a form of steganography: a specific subset of cryptography that involves concealing a secret message within a larger, unrelated message.

This method of secret writing is an ancient one: both the Cardan grille and the usage of the word “steganography” date back to the 16th century. Just because it’s old, however, doesn’t mean it’s obsolete. Steganography is finding new life in our modern age of computers, with messages being subtly slipped into lines of computer code, or even into the arrangement of pixels in a digital image. (And you might even remember an especially amusing example of steganography that went viral and made headlines earlier this year.)

So there’s no denying it — some forms of 18th century spycraft are still alive and well today. I’m definitely hoping to see more excellent examples embedded into tonight’s new episode of TURN.  Stay tuned for another “First Impressions” post after the debut of Episode 2, and don’t forget to follow @spycurious on Twitter for some live tweets during the show!

-RS

Another example of the Cardan Grille system. (Click to enlarge. Source: Wikimedia Commons.)
Another example of the Cardan Grille system. (Source: Wikimedia Commons)

 

 

Watch the TURN premiere online for free!

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Missed the premiere of TURN last night?  Did your DVR malfunction, or do you not even have cable in the first place?  Ne desperandum!  You can now watch the pilot episode for FREE on Amazon Instant Video! Even the HD version is available for free. Spread the word!

amazon episode 1
The pilot episode is available FREE in either standard res or hi-def formats.

No proof of cable subscription required!  All you need is a free Amazon account. Make sure all of your reclusive history-buff friends who have sworn off cable TV (yes, we all have them) see this link so they can get caught up. Now anyone with internet access can join the conversation!

First episode: First Impressions

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pilot final scene

The premiere of TURN is now in the history books! But how much did it actually differ from the history books?  There’s definitely lots to process from tonight’s super-sized 90-minute pilot.  Initial thoughts are below, but since I have an insurmountable affinity for checking historical sources, it’ll be tomorrow (at the earliest) before I’m able to post anything properly analytical.  Overall, I think the premiere was a success — AMC is known for its intricate character-driven drama and TURN fits that mold extremely well.  Any more than that — well, I’m going to sleep on it first, though my half-eaten bag of jellybeans is a pretty fitting indicator of how glued to the screen I was. 😉

cardano grille

The Good: Heavy emphasis on divided loyalties, tension between neighbors, and civilian resentment toward British occupation — all of which muddle the “black and white” myth of the American Revolution, which is a very good thing.  I enjoyed the panoramas of Setauket as a small, agricultural, coastal cluster of colonial buildings. Loved seeing the first hint of spycraft — a Cardano Grille, pictured left. (More on that in a later post.)

The Bad: The Queen’s Rangers take first place in this category.  Material culture issues (ranging from clothing to beards to architecture) ranged from passable and fairly innocuous to cringe-worthy. What bothered me more, however, were the really major chronology issues. Most of the events depicted in this episode didn’t occur until late 1777, 1778, or even 1779.  The Culper Ring wasn’t even formed until 1778, and John Andre doesn’t enter the picture until 1779.  So why pick 1776 as the date for the pilot episode?

The Complicated: While the Revolutionary War was a messy affair, and brutal atrocities were committed by both sides, I’m not sure the uber-violent scenes (and especially the revenge-driven bloodlust) shown here were historically appropriate, and got the impression they were there simply to give the show a more “edgy” feel.  The 18th century was an heavily honor-bound culture; “waterboarding”-like torture is definitely out of place here.  The whole “Bluecoats” vs “Redcoats” dynamic is a out of place for this time period, but I understand why the showrunners chose to portray the opposing armies that way — American uniforms were a confusing mess across the board in 1776.

Oh, and remind me not to enter the stock market anytime soon: My Nathan Hale prediction was a total bust!  I’m actually very disappointed.  If this episode was really supposed to take place in 1776, there were plenty of opportunities to bring up Hale — especially, for example, when Tallmadge was berating his officer about the need to invest money and effort into obtaining proper intelligence.

 

So what are YOUR thoughts on the pilot episode of TURN?  If you’re a history buff, were you satisfied? Or mortified?  If you’re a new viewer with no special background in history (which is perfectly okay, thank you very much!), did the show hold your interest?  Don’t be shy — your comments will help determine the topics that get covered first in this blog!  (All right, if you’re a LITTLE shy you can always submit an anonymous question or comment via the Ask Page.)

-RS