Not to mention their use of antique technology torpedoes that sink their own subs!!
Actually they have supposedly perfected an "underwater missile" design that we had given up on even before they stole it.
It's called the "Squall", it supposedly generates a bubble ahead of its self eliminating the water resistance and allowing a speed of 300 MPH.
Which may seem to poke a hole in my earlier comment.
But it shows they can make other peoples ideas work it's just their own that suck.
Also, I read about this from one source, always reliable, but not confirmed any where else.