Squalus sinking.

Construction of the Squalus began on October 18, 1937, in the Portsmouth Navy Yard in New Hampshire. The Squalus was commissioned on March 1, 1939, under the command of Oliver Naquin. The submarine began a series of test dives near the Isles of Shoals and made its nineteenth on the morning of May 23. The dive was routine until the vessel reached a depth of sixty feet, when the engine rooms began to flood. Twenty-six men died when the after section of the submarine flooded. The Squalus came to rest at a depth of 243 feet, with the bow at an angle of eleven degrees. The Squalus sent up a marker buoy along with signal rockets. While waiting to be rescued, the crew put on their Momsen lungs, which they used as gas masks. The lung recycled exhaled air using an oblong rubber bag containing soda lime.