This is a great piece of submarine history! The "Aluminaut" was the first aluminium submarine manufactured, conceptualized back in 1942 during the second World War. Like many companies, Reynolds turned toward supporting the war effort, despite about 65% of the company's sales being in foil. The actual submersible wasn't made until 1964, however.

The Aluminaut was about 6.5 inches thick, giving it a maximum dive range of 17,000 ft. It has some pretty cool history attached to it as well in the shorter wikipedia post! After the 1966 Palomares B-52 crash over Palomares, Spain, the Aluminaut was one of the vessels that helped search for a missing atomic bomb that landed in the ocean.

The sub is actually on display at the Science Museum of Virginia if you ever get a chance to see it.