Work continues on the aircraft carriers.

I have worked out the tech levels and which ships are available at each level.

If all goes well, this will be my deepest tech tree so far. One of the problems I have been having is that the players have been going all out on technology and running off the end of my tech tree. This one runs up to 1960's level tech, so if the players want to spend all their money on aircraft carrier development they can be building Kitty Hawk Class ships in 1946 if they want.