Could be worse OP, could be a movie about the North Koreans successfully invading America, you know, North Korea, a country that barely has a navy and who’s Air Force is mostly old Migs from several decades ago, a country who starts threatening their neighbors whenever their food supply runs low because their chubby leader eats too much.

At least the original version of the movie was against the Russians while they were a super power.

a country that barely has a navy

North Korea has the largest submarine fleet of any nation. Of course most of those are old diesel subs, but the point still stands.

Diesel subs have some advantages over others, some distinct disadvantages too, but a few advantages

What advantages? If memory serves correctly, they’d need a captain with a penis tattoo that says “welcome aboard” and a radar guy who can imitate whales. I’m not sure that’s so common.

diesel submarines can be quieter than nuclear subs when operating in electric mode, although their range is limited.