Haiphong's Naval Museum is a specialist stop, but it fits the city better than it would almost anywhere else in northern Vietnam. Haiphong is a port first, and the museum gives that maritime identity a military and historical frame.
Expect a modest collection rather than a polished national museum. It is most worthwhile if you are already interested in ships, wartime history, or the way Haiphong's harbour has shaped the city's role between Hanoi and the Gulf of Tonkin.