National Geographic Big, Bigger, Biggest:

At 171 m long, the USS Pennsylvania is the biggest submarine in the US Navy. It can dive deeper than a thousand feet, sail for 20 years without refueling, and remain submerged for up to 6 months. The vessel carries a crew of 155 men and a deadly nuclear arsenal. This film explores how this submarine was made possible through a series of six historic engineering breakthroughs. The film explores the inner workings of six landmark submarines, including the tiny Turtle and colossal German U-Boats. Each features a major technological innovation that allowed engineers to build bigger and bigger submarines.