References

Renovation and improvement of submersible P-63
The manned submersible P-63, with a rated depth of 300m, is operated by Subspirit in Switzerland (https://www.subspirit.ch).
The submesible P-63 has been overhauled and brought up to state of the art in terms of safety and reliably.
For this purpose the external structure including the main ballast tanks and vent valves have been renewed.  The battery systems has been installed outside the pressure hull in new designed pressure vessels.  Further improvements has been made in the propulsion and in the life support systems.
The improvements in weight and space inside the pressure hull allowed for increasing the number of occupants from 4 to 5. 
The overhaul works were mainly done by Abächerli Technik GmbH. Pressure tight battery compartments, manufactured by Jeger JAA GmbH. 
Hydrodynamic and design-optimized outer shells made of CFRP
with walk-out stainless steel deck.
Design of the shell and main ballast tanks was realized in cooperation with Sauber Technologies AG.
CFRP parts were manufactured by Aerolite AG, Horw.  

New main ballast tanks made of CFRP with new, automatically closing, hydraulically operated vent valves made of stainless steel (in-house design by IBH). Valves were manufactured by Sigrist AG.
Weight optimized topstructure made of stainless steel (background). 
Submersible P-63 before Renovation, picture taken in 2022.