You’ve seen it in the movies about WWII, a US navy submarine spends its day resting on the sea floor waiting for nighttime to surface, recharge its electric batteries and begin hunting for Japanese warships or a big fat oil tanker.

These days, US submarines are nuclear-powered and huge by comparison to those used in WWII. and they no longer spend any time sitting on the bottom of the ocean floor. Here is what that is all about.

Before nuclear submarines were developed, they ran on a combination of diesel and electric power and operated mostly on the surface at night and submerged during the day running on electric power stored in banks of lead-acid batteries.  Submarines in the pre-nuclear power age trying to conserve electricity would often sit on the bottom in relatively shallow waters of less than 500 ft and then pop to the surface at night to resume their patrols on the surface.

These submarines were also much smaller in terms of length, and displacement. A US sub of the Gato class in WWII displaced about 2,000 tons of water when submerged while the modern Seawolf class of fast attack subs displaces more than 9,000 tons.  WWII submarines lacked a great deal of the electronic sophistication of modern subs which had numerous openings in the hull to intake seawater to convert it to fresh water and to draw oxygen from it for the crew to breathe. Unlike WWII submarines, modern subs have sensors fitted to various places on the hull including the bottom.

Additionally, the outer hulls of modern subs are also coated with rubber called the Special Hull Treatment to reduce the amount of sound they make in the water.


Seawolf Class Attack Submarine
The Seawolf-class attack submarine USS Connecticut returns to port at Naval Base Kitsap-Bremerton after participating in Ice Exercise 2011 in the Arctic Circle. (Source: Defense Visual Information Distribution Service/getarchive)

Submarines in WWII and even later didn’t have all these sensors and coatings on the hull so they could rest on the bottom in shallow water without too much concern about damaging the hull or its fittings.

This is not to say that sitting on the bottom was something easy to do or without its perils.  The sea floor is not uniformly flat. In WWII, submarines were essentially blind underwater and could not know what was beneath them when they set down.  Later in the war they had sounding sonars than could tell them how close they were to the bottom, but they mostly relied upon charts with soundings taken by hand that were not very accurate at all.