I imagine the biggest difficulty with this is that right now a sub has to be a certain size to be self-sustaining on longer missions. An airplane can get to it's target in a matter of hours but it takes a sub a matter of days. Maybe a larger sub could carry the small one to the field of battle and then one-person would venture out in it.

I also think your idea could allow a man-carrying sub to be small enough to go super-cavitating for a short period, which will allow hundreds of mph underwater. Very interesting--surely this would change the dynamics of a battle. But also, a large sub has a large towed array--the 'fighter' sub would probably not be able to have much for passive sonar. Maybe active sonar would be okay, since it could out-manuevoer normal torpedos anyway.

I know that current French subs (diesel and fuel cell) are very small compared to US nuclear subs, but they still aren't 'fighter pilot' subs, they carry many people.

Also, the Japanese tried mini-subs in WWII with very negative results.

I'm not a navy person; I wonder what a trained navy person would say.

Although this is somewhat off topic the current military realities demand new strategies of a totally different order than refining weapons which were useful in the war between superpowers. The dangers to peace and security lie more in economic and cultural realities than improving technically combative tools against submarines and combat fighter planes.

They don't make small, fast, maneuverable torpedos because there aren't any small subs to shoot them at. If navies start making small fast subs, weapons designers will design torpedos to destroy them.

I thought the reason that things move slower through water than air is that water is a much more dense medium than air. Making something smaller doesn't solve the density problem.

This likely would explain why there are no supersonic watercraft. Or for that matter, exceptionally fast underwater craft.

I think that if it could be done someone would have done it by now. And considering the money that's been tossed into aircraft to speed them along I'd say lack of funding for these watercraft isn't the issue.

One further point. The trend in aircraft fighters is towards total automation with a pilotless craft. I know very little about torpedoes but it probably be more effective in improving the artificial intelligence on board the torpedo than putting a man in danger. Sonar feedback could make them remote controlled but that might reveal the location of the mother ship which is not a good idea.

sand, you're right about tactics changing, but it may be that they'll change back toward midget subs. Apparently they've been tried. Seems Iran has even built one lately.

http://en.wikipedia.org/wiki/Midget_submarine

as for autonomous subs vs. manned, it's hard to communicate underwater and we don't have computers that are smart enough to react at this time. AGV planes aren't really autonomous--they ususally tranmit a real-time TV camera picture and can receive real time control from the ground. Most torpedos are still wire guided for some distance--i expect the ocean floor is criss-crossed with torpedo wires. It might be hard to make a maneuverable sub that's pulling a wire, but it could solve the problem of the midget not having a sonar array if they can give it real data from the mothership. A wire really limits range, too.

As for Hyenuf's comments about water being too dense to make a maneuverable craft, I think it's all relative--the same fluid-dynamics equations apply to subs and planes--just the reynolds numbers are different. The mini-sub might not be impressive, but it could still be stronger/stiffer and have a higher power to drag ratio than a full sub and hence really out-'fly' it, just like a single seat plane out flies a big one.

Here's another interesting sub site I saw about sub yachts:

http://ussubs.com/

Unmanned drone subs might also work, just cameras & sensors with broadcasting. Perhaps a smart program so it can navigate w/o revealing its position as it carries missiles & snoops around. This could give pirates something to think about at a low cost. But then, drone planes are also cheap & getting better, too.