Skills to build the Nautilus (and similar revolutionary vehicles)

[Michael Thayne]

The release of the latest book in the Steampunk series got me thinking about how you'd stat up a Captain Nemo expy. Presumably the Nautilus is an Amazing invention, so by the inventing rules it seems like Nemo needs skill 21+ to invent it. Accordingly, GURPS Adaptations gives Nemo Engineer (Electrical)-21. But shouldn't he also have Engineer (Submarine)-21? It seems like he needs both. On the one hand, the Nautilus' batteries seem like they qualify as an Amazing invention in their own right. On the other hand, it's not like Nemo just took an existing sub design and added special batteries, so the Nautilus itself is a second Amazing invention.

This seems like a common problem for a certain type of fictional character. For example, Star Trek's Zefram Cochrane might need both Engineer (Spacecraft)-21 and Engineer (Warp Drive)-21. Builders of backyard moon rockets might need one skill to design the powerful engine that enables SSTO craft, and another skill for the rest of the design. Something similar might apply to builders of giant mecha (though I'm not well-enough versed in that genre to be sure what the relevant skills are).

Is this analysis correct? Or is there some way you could justify giving such characters just one Engineer specialty at level 21, and let them rely on defaults for the rest of it?