If by “lines”, you mean the flank sonar arrays on the Trafalgar class, they are part of the 2076 integrated sonar system. They are actually slightly raised areas from the hull, containing numerous hydrophones. The submarines were also covered with sound absorbing anechoic materials.

They look like lines in the one OKB photo . I have not seen the kit in person, as I don’t build 1/700 scale. Eyes no longer decent enough for smaller scale.

Tom