In a cold underground bunker once packed with enough dollars to replenish the cash supply in the eastern United States in the event of a Soviet nuclear attack, "Gigi" lies silently near "An American in Paris".

In a room next door, a young woman who gave her name as Barbara works on "Little Brother". Upstairs, one of Barbara's colleagues is trying to make sense of "The Arab".

This is not a secret US interrogation site, but the state-of-the-art facility where the US Library of Congress holds and preserves the world's largest collection of films, television programs, radio broadcasts and sound recordings.

Last year, the four-million-piece collection at the National Audio-Visual Conservation Center (NAVCC), which includes 700,000 reels of film, swelled immeasurably in historical terms as Russia handed over digital copies of 10 US silent movies that were thought to have been lost.

"The Arab", directed in 1924 by Rex Ingram, who made a star of Rudolf Valentino in "The Four Horsemen of the Apocalypse" a few years earlier, was one of the films returned to the United States by the Russia's state film archives, Gosfilmofond.

In the 1920s, movies were made on film containing nitrate, a highly unstable and flammable chemical compound that sparked fires in cinemas when projectors ignited while playing movies.

A study conducted some 30 years ago showed that about 75 percent of all US films produced during the silent-movie era have been destroyed or survived only in fragments.

The same study found that most of the old movies from the silent era that have survived intact are held in foreign archives, not American ones.

"American studios were turning out movies like sausages, and selling them around the world," Patrick Loughney, director of the NAVCC, told AFP.

"The attitude here was, if you like one Fred Astaire film, wait six months and there will be another one out. Foreign countries that we sold the movies to looked after them better than we did," he said.

A brisk trade in US movies sold to Russia began in around 1910 and continued through the Soviet era right up to the outbreak of World War II, Loughney said.

"The records we have indicate that over 1,300 US feature films were distributed in Russia during that period," said Loughney.

The Russians took "great care" of the old films, returning to the United States high-quality digital copies of the 10 silent movies that could be transferred to 35-millimeter film.

But before that happens, the NAVCC wants to restore the original American inter-titles -- the frames in silent movies that show the dialogue -- of the movies.

At the moment, in the copy of "The Arab" returned by Russia, Ramon Navarro, who starred in the movie as a young Bedouin in love with a Christian missionary's daughter, "speaks" in Russian Cyrillic script.

NAVCC sleuths are "looking in archives around the country to find the original American language inter-titles, either in scripts or cutting continuities that date from the era," said Loughney, comparing the pain-staking work to archeology.

"If we can identify those and bring them back to the library, we can recreate the American language inter-titles, take out the Russian language intertitles and ultimately restore the movies to as close an approximation as we can of what American audiences saw when they were released."

Russia isn't the only country that has sent US-made movies back home.

New Zealand has sent back several movies and the NAVCC is working with the Centre National du Cinema in France to ship some 20,000 reels of early US-produced films for safe-keeping at the bunker-turned-archives, carved into the hillside in Culpeper.

"We suspect that there are quite a number of lost films among those films in France," said Loughney.

The nine other films returned to the United States by Russia were "Canyon of the Fools", "Circus Days", "The Conquest of Canaan", "The Eternal Struggle", "Keep Smiling", "Kick In", "Valley of the Giants", "You're Fired" and "Call of the Canyon", which was the only one of the 10 that was incomplete.

"Gigi" and "An American in Paris" are among hundreds of thousands of reels of film held in the NAVCC's master film vault, where the temperature is kept just above freezing.