1968 was a busy year for both U.S. and Soviet navies. USS Pueblo captured by the Norks on January 23, Soviet submarine K-129 lost on March 8, USS Scorpion lost on May 22. And a fair amount of naval activity around Vietnam.
Some conspiracy-minded folks have suggested that the Scorpion was sunk by the Soviets in retaliation for the loss of K-129, which some figures in the Soviet command blamed on the U.S. Not saying I buy the theory . . .