Quote Originally Posted by DrWho2010 View Post
the prototypes designs are unlocked from the schematics board in the workshop. you will the need the items gained from sub ventures (or airship ones if you ever did those) to unlock the higher level parts.

the easiest way to get those is to trade for the items to unlock the schematics. they are not sell-able on the market board so you will have to put up a pf to trade for them or you can join the submarine discord and peruse the trade channels there.

if you insist on doing it yourself be warned it will take a lot longer as you will be subject to RNG of loot on return, provided you know where to send your subs to get them and that you have the proper stats to obtain them.
Oh dear. So I am just subject to bad RNG >.<.
Thanks for letting me know ^_^.