MOSCOW — The Kremlin’s chief spokesman has confirmed that a report broadcast on Russian television this week revealed the design of a secret nuclear weapon delivery system: a drone submarine that could attack coastlines.

Russian officials said the revelation of the submarine, which has not yet been produced, was accidental. But it came to light in the Russian news media in a way that suggested that the Kremlin wanted the West to know.

Such a submarine design had been conceived decades ago, independent Russian military commentators said, but it had not been revealed until now. It would function as a long-range torpedo and would avoid missile defenses by traveling under the ocean’s surface.

News of the design was reported on state and NTV television on Monday as though merely in passing, during a meeting between President Vladimir V. Putin and military industry officials and generals. The broadcast began with a public portion.