ROBERT SIEGEL, host:
Two months ago, the last living U.S. veteran of World War I died, and this week, another milestone of that long-ago war: The CIA released six secret documents from 1917 and 1918. They were the oldest papers still labeled classified by the U.S. government.
NPR's Rachel Martin reports that the documents themselves don't reveal big secrets. Instead, they describe the art of keeping them.
RACHEL MARTIN: Dip a toothpick in milk and write between lines of an ordinary letter. When the paper is heated, like with a flatiron, the writing will appear. Or if you prefer the German style, instructions are as follows: Mix an ounce of aluminum and one ounce of white garlic juice. Write with a quill. When the paper is heated, the letters appear. Sure, kind of sounds like Ralphie in "A Christmas Story" with his secret decoder ring. [POST-BROADCAST CORRECTION: The German formula for invisible ink actually used alum, not aluminum.]
(Soundbite of film, "A Christmas Story")
Unidentified Man #1 (Actor): (As character) Remember kids, only members of Annie's secret circle can decode Annie's secret message. Remember, Annie is depending on you.
MARTIN: But back in World War I, passing secret messages was a matter of life and death. And the U.S. government has held onto these secrets for 93 years.
Ms. SHERYL SHENBERGER (Director, National Declassification Center): As you can see, we've protected them appropriately.
MARTIN: And these are the original documents?
Ms. SHENBERGER: These are the originals.
MARTIN: That's Sheryl Shenberger. She's the director of the National Declassification Center in College Park, Maryland. There are tens of millions of secret documents here in this building, now declassified. She proudly shows off the latest additions: old, worn papers, some typed, some handwritten.
Ms. SHENBERGER: You can see the method that's used, the kind of equipment, the kind of material. They go into some very nice detail.
MARTIN: The documents also shed some light on how these messages were delivered. One, titled "Secret Writing," says a certain invisible-ink concoction can be carried around in starched shirts. Shenberger explains.
Ms. SHENBERGER: It's a chemical. It would be in the starch. What a covert way of carrying something. Who's going to look at the starch in a collar? Again, for those of us who enjoy that kind of spooky stuff, that's kind of cool.
MARTIN: The CIA has been managing the declassification of secret documents since the agency came to be in 1947. As to why it took so long for these documents from the First World War to be released, the CIA says that only recently has this particular aspect of spycraft become obsolete.
A CIA spokesman said, quote, "in recent years, the chemistry of making secret ink and the lighting used to detect it have greatly improved."
Sheryl Shenberger of the National Archives says the tendency when dealing with national security secrets is to err on the side of caution.
Ms. SHENBERGER: Because it's taken a long time for these to see the light of day, so to speak, that gives us some indicators too that this methodology developed way back still had relatively current use.
MARTIN: Which makes you wonder if all this time, covert operatives around the world have been sending secret messages with nothing more than milk and a good quill pen.
Rachel Martin, NPR News, Washington.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.