WASHINGTON — More than 80 years after the end of World War I, the United States still won't give up the secrets behind a surreptitious tool used by the Allied forces: invisible ink.
A public interest group filed a federal lawsuit this week as part of a three-year campaign to gain access to the nation's oldest classified documents, papers that date to World War I and bear such tantalizing titles as "Secret Inks," "Detection of Secret Ink," "German Secret Ink Formula" and "Pamphlet on Invisible Photography & Writing."
Last week the group broadened its quest to include a copy of the "Secret Ink Technical Manual," a 1945 report prepared by the government's Office of Censorship. That report updates the history of secret writing with details from World War II.
But government lawyers aren't budging. They're claiming in court filings and correspondence that release of the papers could compromise national security.
"Come on, these are baby games," said Mark S. Zaid, a lawyer for the James Madison Project, a nonprofit organization that aims to reduce secrecy and promote government accountability. "These secret inks are well-known. Any idiot, just by spilling water, could figure out there's secret ink there. What are they hiding?"
In papers filed in U.S. District Court, Zaid has described secret ink writing as "a fascinating but arcane science which today is more often the subject of comic book and cereal box advertising than spy craft." He said that the classified materials undoubtedly involve basic formulas that for decades have been in the public domain.
The legal battle over secret ink began in 1998, when the organization asked the National Archives to identify the oldest classified document in its custody.
Officials responded with titles and dates of six documents dealing with secret ink. But they didn't release the materials, saying that decision was up to the CIA. The CIA refused to release them, leading to a suit against the government pending before Judge Thomas Penfield Jackson. Jackson also wound up with the case that was filed this week.
In court papers on the earlier lawsuit, government lawyers have said that enemies of the United States do not know which particular formulas and methods the CIA considers reliable. They said secret inks remain viable for use by CIA case officers and sources.
"The age and availability of information about the science of secret ink does not diminish the value of keeping secret the particular formulas and methods at issue here," government lawyers wrote in asking Jackson to dismiss the original lawsuit.
The new lawsuit covers similar legal ground. The National Archives provided Zaid with a copy of the 1945 report, but it was filled with redactions. Most of the excised material appeared to involve compounds used to make invisible ink and methods used to detect it.
The sections made public included one on the history of secret ink, tracing its use to 230 BC. Over the centuries, the manual said, a variety of substances were used with varying success, including fruit juices and cobalt salts that could be developed and detected through heat or light.
The manual goes on to state that more sophisticated methods were in place by the advent of World War I, saying that secret inks were frequently used in communications by both sides and that "all the intelligence laboratories of the various countries were soon at work on the problem."
CIA spokesman Mark Mansfield said he had not seen Zaid's latest lawsuit and declined comment on the litigation. But he said the CIA has no intention of keeping papers secret unless there is a "legitimate, well-grounded reason."
"We also don't want information that would be useful to terrorists and others who wish to harm Americans out in the public domain," Mansfield said. "Just because a document is dated doesn't mean it has lost its usefulness and sensitivity. It could be very useful to someone who wishes to communicate secretly and do harm."