The Kremlin has admitted plans for a top secret, long-range nuclear torpedo were shown on television news by mistake.
Two Russian TV channels broadcast a large document, filmed over a military officer's shoulder during a meeting with President Vladimir Putin, showing drawings of a weapons system called 'Status-X'.
The submarine-launched torpedo system is described in the document as 'devastating'.
Launched by a submarine, it would create "wide areas of radioactive contamination", the document said.
The "oceanic multi-purpose Status-6 system" was designed to "destroy important economic installations of the enemy in coastal areas and cause guaranteed devastating damage to the country's territory by creating wide areas of radioactive contamination, rendering them unusable for military, economic or other activity for a long time", the document said.
"It's true some secret data got into the shot, therefore it was subsequently deleted," said Mr Putin's spokesman Dmitry Peskov. "In future we will undoubtedly take preventive measures so this does not happen again."
However, the Russian government newspaper Rossiiskaya Gazeta later reported details of the weapon, without showing the diagram, and speculated about a super-radioactive cobalt device. So the leak may not have been accidental.
On the diagram the giant torpedo's range is given as "up to 10,000km" and depth of trajectory is "up to 1000m".
It was developed by Rubin, a submarine design bureau in St Petersburg.
It would, apparently, be launched by nuclear-powered submarines of the 09852 "Belgorod" and 09851 "Khabarovsk" series.
Rossiiskaya Gazeta called the torpedo a "robotic mini-submarine", travelling at 100 knots (185km/h), which would "avoid all acoustic tracking devices and other traps".