WASHINGTON • A few months after the collapse of the Soviet Union, a group of American investors and Russian scientists struck a deal to begin marketing one of the crown jewels of Moscow's strategic arsenal: An entire family of missiles designed for launch from submarines.
Up for sale were powerful missiles called Calm and Ripple, built to lob heavy warheads into space from a barge or a submarine tube, and a new model called Surf that could be rolled off the side of a ship and fired straight out of the water.
The idea of the joint venture, as one of its US partners wrote in early 1993, was to link American satellite companies to a top Russian weapons laboratory to "convert potentially threatening submarine missiles into peaceful space boosters".
The Americans quickly ran aground on a series of legal and bureaucratic barriers, but the Russians forged ahead with a new partner willing to pay cash for Soviet military technology: North Korea.
More than two decades later, some of the Soviet designs are reappearing, one after another, in surprisingly sophisticated missiles that have turned up on North Korean launchpads over the past two years. Now, newly uncovered documents offer fresh clues about the possible origins of those technical advances.
North Korea is known to have relied on Russian parts and designs for its older missiles, including the Scud derivatives that had dominated its stockpile since the 1980s.
The documents from the Makeyev Rocket Design Bureau include technical drawings for much more advanced missiles - designs that include features seen in some of the newest missiles in North Korea's expanding arsenal. Marketing brochures for an array of top-of-the-line Soviet missiles that were able to deliver nuclear warheads to US cities were also found.
Initially designed for the Soviet navy's nuclear submarines, some of the models offered for sale could be launched from a large boat, a submerged barge or a capsule dropped into the ocean, negating the need for a modern submarine fleet.
The evidence that the designs eventually ended up in North Korea is partly circumstantial. In the summer of 1993, with the US-Russian project flagging, more than 60 Russian missile scientists and family members from the Makeyev facility were arrested at Moscow's Sheremetyevo International Airport as they prepared to travel to Pyongyang to work as consultants.
US, Russian and South Korean intelligence officials later concluded that some of the scientists eventually succeeded in travelling to North Korea to offer blueprints and technical advice for the country's missiles programme.
But US analysts see more persuasive evidence in the actual missiles that North Korea has put on display over the past two years.
In the most striking case, the Hwasong-10, or Musudan, a single-stage missile successfully tested by North Korea in June last year, appears to use the same engine and many design features as the Soviet Union's R-27 Zyb, a submarine-launched ballistic missile designed by Makeyev scientists. Two months later, on Aug 24, the North successfully tested the Pukguksong-1, a submarine-launched missile that also incorporates some of the same features as the Zyb.
Both models are "generally regarded as derived from the designs of the Makeyev Bureau's R-27", said Mr Joshua Pollack, an analyst at the James Martin Centre for Nonproliferation Studies.
Those two tests were followed in recent months by even greater technological leaps, culminating in the successful tests this year of North Korea's first true intercontinental ballistic missiles, capable of reaching every city in the continental United States.
The fact that it has taken Pyongyang so long to exploit the Russian designs is perplexing, but North Korea had long lacked the sophisticated materials, engineering expertise and computer-driven machine tools for the kinds of advanced missiles it has recently tested, weapons experts say.
With an industrial base enhanced by years of slow, patient acquisition efforts, North Korea is only now in a position to capitalise on technology it had been sitting on for years or even decades, analysts say.