FWIW, submarine patents are long dead, so it is possible to feel assured that old enough stuff is patent free. Of course that denies a lot of important improvem

FWIW, submarine patents are long dead, so it is possible to feel assured that old enough stuff is patent free. Of course that denies a lot of important improvements, but due to diminishing returns and the ramp of tech development it's still ever more significant. A lot of key stuff is going to lose monopoly lock this decade.