[3] The EB design retained the semi-hemispherical rotating bow cap that covered the four 18-inch diameter torpedo tubes.

[4] The Lake design used individual muzzle doors with hydro-dynamic shutters to seal the tubes, a feature that would become standard on all later USN submarines.

[5] These boats were big enough to have a semi-retractable 3-inch/23-caliber gun on the deck forward of the conning tower fairwater.

His design for the follow-on R-class boats would abandon the method in favor of the EB angle-diving arrangement.

[8][9] CALSHIP suffered from numerous management and production issues and all three boats assigned to them had to be towed up the coast to the Mare Island Navy Yard north of San Francisco in Vallejo, California for completion.

[10] The class originally operated in the anti-submarine role off the United States' East Coast.

The steamer scored six hits on O-4's conning tower fairwater and pressure hull before her identity was discovered.

However, the decommissioned O-12 was leased back to Simon Lake for use in an Arctic expedition by Sir Hubert Wilkins.

[12] The EB design boats served well although O-5 was rammed by a cargo ship and sunk near the Panama Canal on 28 October 1923 with the loss of three crew members.

The harsh economics of the Great Depression prevented proper pre-layup maintenance, and very little if any work was done on the boats during the nine years they laid in reserve at the Philadelphia Navy Yard.

The looming war emergency forced the work to be rushed, and many of the eight O-class still needed thorough maintenance after being recommissioned.

O-9 sank during deep submergence trials in June 1941, likely due to her poor material condition.