Swedish investigators took logbooks and instruments from S-363 and adapted a Coast Guard vessel to check the diesel submarine for nuclear material. Diesel propulsion did not rule out nuclear armament, since Soviet diesel boats were known to carry nuclear torpedoes. The measurements reportedly registered something, although the discussion does not identify the result precisely. S-363's political officer later said that a Swedish attempt to seize the submarine would have led the crew to destroy it, including the warheads. That reported contingency added a nuclear-weapons risk to decisions about boarding and taking control of the grounded boat.
Notable Point · 20:28-21:49
The nuclear-weapons risk in the S-363 crisis
Swedish checks for nuclear material and a reported Soviet contingency to destroy S-363 raised the stakes of any attempt to seize the grounded submarine.