The United States Navy's sixteen O-class submarines were created out of the lessons learned from the L class. The O class were about 80 tons larger than the L class, with greater power and endurance for ocean patrols. Due to the American entry into World War I the O class were built much more rapidly than previous classes, and were all commissioned in 1918. O-1 through O-10 were group 1, designed by Electric Boat, O-11 through O-16 were group 2, designed by the Lake Torpedo Boat Company and sometimes considered a separate class. The group 2 boats entered service just before the end of World War I. Eight of the group 1 boats survived to serve in World War II as training boats when they were recommissioned in 1941.

The Portsmouth Naval Shipyard, often called the Portsmouth Navy Yard, is a United States Navy shipyard on Seavey's Island in Kittery, Maine, bordering Portsmouth, New Hampshire. The naval yard lies along the southern boundary of Maine on the Piscataqua River.