>>15765056
The movie took place later (book published in 1984, movie in 1990) and the submarine had a unique electromagnetic caterpillar drive.
From the movie website:
"In November 1984, the Soviet Union's best submarine captain, in a new undetectable sub, violates orders and heads for the U.S. The American CIA and military must quickly determine: Is he trying to defect, or to start a war?"
https://www.imdb.com/title/tt0099810/
There were subs lost in 1968:
INS Dakar
Minerve S
K129
USS Scorpion
https://www.wearethemighty.com/mighty-history/1968-was-the-deadliest-year-for-submariners-post-wwii/