I recently watched "Azorian" via Amazon Prime streaming. It's about
the CIA's program to raise the Soviet sub K-129 that sank off of Iceland
in 1974.

Talk about some serious engineering! Howard Hughes was recruited to
provide a cover story by "financing" the design and building
of the Huges Glomar Explorer as a sea bed mining ship. In reality the
CIA financed it all of course.

The bottom of the ship had two huge doors that slid open
allowing the deployment of a giant lift device with claws that would
submerge, held in place by pipes, to a depth of 16,500 feet where the
sub lay on the bottom.

The technical challenges of designing the systems involved were mind
boggling. Makes the challenge of going to the moon look like duck soup.

Great documentary for those with this kind of interest.