The voice interception program, called MYSTIC, began in 2009. Its RETRO tool, short for “retrospective retrieval,” and related projects reached full capacity against the first target nation in 2011. Planning documents two years later anticipated similar operations elsewhere.

In the initial deployment, collection systems are recording “every single” conversation nationwide, storing billions of them in a 30-day rolling buffer that clears the oldest calls as new ones arrive, according to a classified summary.

The call buffer opens a door “into the past,” the summary says, enabling users to “retrieve audio of interest that was not tasked at the time of the original call.” Analysts listen to only a fraction of 1 percent of the calls, but the absolute numbers are high. Each month, they send millions of voice clippings, or “cuts,” for processing and long-term storage.

At the request of U.S. officials, The Washington Post is withholding details that could be used to identify the country where the system is being employed or other countries where its use was envisioned.

No other NSA program disclosed to date has swallowed a nation’s telephone network whole. Outside experts have sometimes described that prospect as disquieting but remote, with notable implications for a growing debate over the NSA’s practice of “bulk collection” abroad.

read more: http://www.washingtonpost.com/world/national-security/nsa-surveillance-program-reaches-into-the-past-to-retrieve-replay-phone-calls/2014/03/18/226d2646-ade9-11e3-a49e-76adc9210f19_story.html?hpid=z1

Picture at top is the "cover slide comes from a weekly briefing deck by the NSA's Special Source Operations team, which is responsible for deploying and maintaining bulk collection methods."