[IMDB] The film is about a war patrol of a Soviet submarine of the Northern Fleet, tasked with finding and eliminating German fuel supply ships before a Big Offensive can be launched against Murmansk.
Film is in Russian, but it is translatable, and the translation is quite good.
As I have written elsewhere, combat operations involving the Soviet Northern Fleet and naval aviation, and its efforts to aid incoming supplies from the Brits was practically a separate war unto itself.