Naval Ship & Submarine Propulsion Systems

[Vivendi]

A combination of various technologies that are still in early development could make submarines that relies on batteries only much more attractive. A lot of research is ongoing to increase battery energy density to 1,000 Wh/l and above. However in addition some interesting development is ongoing into high temperature superconducting electric engines:

Toshiba announced in June last year on developing a prototype for a compact, high-speed superconducting motor with a maximum output of 2 MW, bringing together its manufacturing technology for high-speed rotating machines and superconductivity technology. The newly developed superconducting motor weighs only a few hundred kilograms, has an outer diameter of about 50 cm, and an overall length of about 70 cm (excluding the shaft), which is “less than one-tenth” of a motor with the same level of power output.

Toshiba Asia Pacific | Toshiba develops a lightweight, compact, high-power superconducting motor prototype for mobility applications – contributes to carbon neutrality in industries and transportation.

 

[Vivendi]

Things are moving ahead, Amprius has already announced a 1,300 Wh/l battery: The All-New Amprius 500 Wh/kg Battery Platform is Here | Amprius Technologies
THey are also planning to build a GWh factory... so prices will come down.

I tried to find the efficiency of HTS motors -- seems around 99%, give or take.
Fully Superconducting Motor Prepares for Testing | Engineering.com
Microsoft Word - 1_MAIN_F-0013-IEM-02-2022.docx (ntnu.no)

However one thing I did not consider is if the cryogenic pumps will create acoustic noise -- I bet they will. Still, if that can be handled, one could most likely build an all-electric submarine with some quite impressive performance characteristics, and not too far into the future either it seems.