I may have seen the movie twice, and I don't believe I've read the book. What are the similarities?
The book contained some good scenes they left out of the movie. The "attack" on the Soviet surface forces by the A-10 Warthogs from the Maryland ANG comes immediately to mind.
The book also had the Red October hiding out in the Pamlico Sound near Ocracoke Island, NC. I grew up near there and there is no way a sub of that size could get into the sound on the surface, much less submerge again.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
In the former Soviet Union, the Political Officer is an officer attached to a unit, usually outside the regular chain of command, who ensures that the regular soldiers and officers obey orders and conform to the government's ideology.
In day-to-day affairs the Political Officer roots out dissenters and has them re-educated or executed, perhaps doubling as a member of the Secret Police or Culture Police.
Contrast this to the HR Department, which is outside the profit center of the company, that ensures that the regular employees and officers of the company obey HR directives and conform to the company's ideology.
In day-to-day affairs, HR roots out dissenters and has them re-educated or terminated, doubling as the "secret police" or "culture police."