[sitharus]

It is, so it’s taken really seriously. The hulls are made from material with well characterised gradual failure modes - bending and deforming rather than sudden failure. This means metals with thoroughly inspected welds and joints to ensure no internal voids, and a process of gradually diving deeper to check the hull meets the design requirements.

Using materials that fail plastically and gradually increasing depth trials means the failure mode is hopefully deformation rather than complete failure, and will happen at the highest depth as possible so a quick surfacing can be achieved.

Submarines, along with space, are an area where innovative new methods need a lot of testing before you commit human life to it.

[jemmyw]

If I remember the early reporting correctly, this submarine had plastic deformation on every dive. So it was already failing, they just didn't do anything about it.