Personally I like PT boats and sea planes... so why not making a map which focuses on a symmetrical battle about an atoll and sea flags which have to be conquered with a balanced team of PT boat sailors and submarines + the air support of sea planes equipped with water bombs?
ach team (US navy & Japanese Marine) start on an own little island where pt boats, subs, and sea planes spawn.
this sounds very similar to Run_Silent_Run_Deep-1943 from FH Fanmappack7/Battle of the Atlantic
maybe take a look at it
i wanted to add it to fhsw mappack anyway