Midget submarines role in the naval warfare is limited primarily because of their size. A midget submarine is generally less than 150 ft. long, about 7 to 8 ft. in diameter, of around 100 – 130 DWT displacement and is capable of carrying about 15 -20 sailors.
Because of the lack of space for fuel, air & water and food for the crew; midget submarine range & duration is severely limited. While the midgets can dive down to 100 meters; understand average under water duration of a midget sub is limited to 10 -12 hours only. Thus they can't travel too far on their own and need a mother ship / support vessel to extend the range.
Nevertheless, since sonar returns are cluttered in shallow water, midget subs can be very useful for sneaking into harbours, laying mines and inserting commandos on beaches. Iran has about 21 midget submarines but then most of her sea coast lays in the narrow Persian Gulf where short range of midgets is not an impediment. In Pakistan’ case, where most of the coast line opens on to the Indian Ocean, a handful of midget submarines should be more than enough.
However, I have across two modern technologies that are being developed for the deep ocean submersibles. One being the remote control technology and other an AIP system based on liquid oxygen. These developments may be for the scientific research but nothing stops one from installing the same on a midget submarine. Since there would be no crew, all the space could be used for more fuel and liquid oxygen considerably increasing the range and under water duration.
Obviously, a torpedo firing remotely operated midget sub barely larger than a large whale, lying in wait 200 miles off shore to ambush enemy warships would be a deadly foe. A fleet of 6 such advanced remotely operated midgets with AIP in the Pakistan Navy arsenal would present a formidable challenge to anyone attacking Pakistan from the sea.
Some brilliant ideas and thoughts. Thanks for sharing your refreshingly out of the box thinking. Here is what I think -
The PN is focused on area denial and anti access but also wants to provide a punch. The success of the Azmat class as a platform is in this - it can not only protect the EEZ but also punch out against the nearby IN ports and bases.
A small midget submarine - not too small - about 600-700 tons would be able to do the same underwater, while saving valuable foreign exchange and could even prove to be an export like the JF-17.
Submarine technology has evolved - a midget submarine can have as little as 4 crew members! One even sees this now in surface ships like the Azmat where far fewer crew is needed than yester yars. It would be an ideal KISS project like the JF-17 (keep it simple st...) not trying to make a world beater but a good enough capability.
With a crew of only 4 and a simple liquid oxygen AIP like you suggested, such a vessel would have excellent range and ability to sustain operations, despite being so small.
It could be armed with simple, port reloadable only torpedo tubes (say 4)
A simple sonar.
A few sea mines (say 2-4)
Sitting near an Indian port (such as near Mumbai), it would be nearly impossible to detect because of its small size. Magnetic anomaly detectors won't find it, nor sonars which would simply equate it to a large rock.
And an idea I had in mind but didn't share before, but am encouraged to by your excellent post - a detachable unmanned attack subsurface vessel.
This would be a much smaller ship with two torpedoes, that will be used as a one way trip weapon, sent to an area (such as an Indian port) on a hunter killer operation. It would basically be a giant torpedo with a small sonar, that will go active at a designated time, and fire away its two torpedoes at anything that it finds moving. If it finds nothing it will go passive and sit and wait until something shows up. This would be for the kind of suicide mission we wouldn't want to send the manned submarines to.
