Slitherine

I modded the battleship shiptype (increased cost, less of a speed penalty) and the human race battleship template and it worked fine in game. I then got a bit ambitious and created a category, massiveship that I then linked to the battleship shiptype. I went into equip.all and created new versions of everything but missiles (no missiles allowed! i.e. I'm lazy) for massiveship.
I started a new game.
Everything seemed to work fine. My AI opponents build the new dreadnaughts and used them. I designed my new dreadnaught (26 grav upkeep!).

But when I go to a planet to build it it does not appear on the list.
If I go back into shiptype and change it back to giantship everything is fine.

I cannot find the function that allows build new ship (text file 559?) anywhere in modkit and am at my wits end in how to build my new titan.

From my point of view, you do not need touch the .a files from modkit. Because my head is a bit bad and you do not explain things too clear, I am not what you made. Have you made a new ship in the ShipBody.all with a new type in ShipType.all? a new shiptype will be unlock by some tech.