SUBSAFE covers all systems exposed to sea pressure or critical to flooding recovery.
They require certification with traceable quality evidence which track the item from the point of manufacture (including all records of the creation of the product, i.e. source materials as well as smelting and hardening process for metals) to the point of installation within a SUBSAFE boundary.
[1] On 10 April 1963, while on a deep test dive about 200 miles off the northeast coast of the United States, USS Thresher (SSN-593) was lost with all hands.
It included addressing the following issues on Thresher: SUBSAFE certification is carried out in four areas: Design, Material, Fabrication, and Testing.
During each step, quality evidence is collected, reviewed, approved, and stored for the life of the submarine.