what's least submarine in the world and can we built a submarine with long distance cominucation?

Answer 1

The Smallest Submarine in the World

With a diameter of 650 µm it finds place in the narrowest chanels. It's
driven by a rotary magnet and allows a voyage of discovering even in the
smallest space.

This submarine, manufactured by microTEC, Duisburg, puts the vision of the
microsystem technology in practice and offers for instance absolutely new
vistas for medical diagnostics. Featured with sensors it could realize
completely new methods for examinations, that are extremely gentle for the
patients.

For the manufacturing of the micro submarine the new features of RMPD
(Rapid Micro Product Development) are used to integrate different materials
seamlessly. Mini magnets, that are fitted in the screw, build the
foundation for the driving system oft the submarine.

You see this smallest submarine in the world at the Hannover Industrie
1998,
H18, 1. OG, M06 from 20.-25. April.

The Micro Submarine:
Rotary Diameter 10µm (micro meter)
Screw Diameter 600µm (micro meter)
Hull Diameter 650µm (micro meter)
Total Length 4mm

Answer 2

Not sure what you mean by least submarine. As far as communication go, the USN already has had for some time a system know as ELF, Extremely Low Frequency, for communicating to submerged submarines. For ship to shore, the sub has to trail an antenna, although I wouldn't be surprised if they had some knid of burst, bounce off a satellite communications technology.

The system is so slow that ELF communications are in letters, letter proximity, and letter combinations.

Answer 3

Least as in smallest?

There's a home-built sub on display near the Hyde Street Pier in San Francisco. Built by college students out of a 250-gallon (or 500?) propane tank. Electric trolling motors, ballast, windows. Crude but clever and it worked when then went down in Lake Tahoe. That should be enough to google on.

Of course, if it displaced 250 gallons, it weighs 2075 pounds.

All I know about sub communications, I read in Hunt for Red October. And Tom Clancey was what?, a real estate agent or something. But apparently he got most things right and discusses the very-low frequency communications they send to Navy subs (like a few hertz so a sentence would take minutes to transmit).