Thanks Guys
We are hoping some people will bring their own subs.
Like they said they would

But we are accounting for the nature of wargamers by ensuring we have enough contraptions. Between me and my brother we are building contraptions for six players.
We have a basic, one pager, set of rules but have still to play test them. Will post them up after we have done that, to get other peoples input.
We also have another one pager on sub design rules, Again we will post them after a play test. Basically each sub is allocated points. The points can then be spent on five or six important systems on the sub e.g. engines, weapons, hull etc The more points spent means that system is better but to the detriment of other things, if you make it too good.
The basic design rules should allow just about any kind of sub design.