It was found in tests that the unusually long engine room was liable to collapse, so there were extra large frames in this section, which proved to be something of an operational inconvenience.

[1] This was in part due to careful attention to detail in the mounting of machinery, and advances made in propeller design to prevent cavitation.

However, grooves were cut into the propellers and injected with a damping filler which cured the problem; Rorqual was later able to surface undetected off the Statue of Liberty.

The Porpoises were far more capable than previous submarine classes in operating for prolonged periods, thanks to much improved air recirculation and cleaning systems.

The Oberon-class submarines, which were almost identical to the Porpoises, and the first of which was commissioned in 1961, survived their predecessor only a little longer, all being decommissioned in the early 1990s.