'97 was 25 years after the original patent was filed, so the original patent was well expired. I would guess that what they were buying from the Navy were lit

'97 was 25 years after the original patent was filed, so the original patent was well expired. I would guess that what they were buying from the Navy were literally just the implementation notes, because even if the patent covers all of the original, key, patent-able ideas, it can still be a bitch to go from that to an actual working implementation.