From Jim Webster
Watermarked PDF – $3.88 USD
Designed as a supplement to Hellfire. 'Boldly going' where Hellfire had too much sense to go. It's not intended to be a free-standing set of rules in itself. This supplement covers actions fought under, on and over water, with emphasis on the activities of submarines and other submersibles.
As well as extra rules to use with Hellfire, there are also three scenarios, two of which are written to be solo campaigns (but can also be played against opponents).