It was called "Operation Behemoth".
Surface and submarine naval exercise. Operation Behemoth (English:hippopotamus)-1 and Behemoth-2 were military exercises held by the Soviet Northern Fleet. Behemoth-2 was the first time a nation's ballistic missile submarine launched all of its missiles at once. The Soviet Northern Fleet had many Ballistic missile submarines by this time.
It was for a few days in 1989 and 1991.