Absolutek is right: I've seen RC sub models of the various Starships Enterprise (NCC-1701-A and 1701-D that are -really- cool!), an rc sub space shuttle, a space battleship Yamato sub, and others... basically, if you think you can make a submarine out of it, chances are you can... provided you're willing to sink the necessary time, engineering, and money into it in order to make it work.
In response to the original question, there are a plethora of resources available in order to build RC submarines, and if you want to do it yourself, http://www.subcommittee.com is a great resource because of their supremely organized devotion to the hobby: these guys are to submarines what we are to fast gun/big gun combat. Also, there are numerous off-the-shelf German, American, and Russian submarine model kits available online or in local hobby shops that can be converted to RC purposes without spending over a thousand dollars: a really popular kit is the 1/72 Revell Gato-class American submarine. I think there is an equivalent Type-VIIC U-Boat kit as well. However, if you want to build big, such as 1/96 or larger, expect your final bill to be between $700 and $2000 from project start to project operational as a functioning submarine... basically about the same cost as a Class-3 to Class-7 ship fully rigged out as a combat vessel. If I had the money, time, and space to do so, I'd have one of those immense Typhoon-class submarine kits available from http://www.engel-modellbau.de - this company has probably the highest level of niche-market commercially built model kit detail I've ever seen, and I've compared kits from Robbe, RC Subworks, and others. Their kits are quite literally the very last word in RC Submarine technology and versatility. The problem is, they are also extremely expensive by comparison to an RC surface warship, that for less money can be turned into a functional weapons platform that is far more versatile in terms of enjoyment than a submarine.
I still think RC submarines are cool, and one day I plan to build one... but I have a class-7 Battleship to finish, first.
