On October 13, 1915, the monitor , a submarine tender, and 4 submarines arrived in Groton, CT. With the war effort in Europe and the Atlantic in full swing, additional submarines and support craft arrived the following year and the facility was named as the Navy's first Submarine Base. Although physically located in Groton, CT, the base had their main offices and housing in the larger city of New London, hence was christened as Naval Submarine Base New London. Following World War I, the Navy established schools and training facilities at the base.
On January 21, 1954 the first nuclear-powered submarine, the , was launched from Groton. In 1982 the Nautilus was designated a National Historic Landmark in Groton. It is permanently moored south of the main gate, attached to the U.S. Submarine Force Museum. Self guided tours are available to the public every day except Tuesday.
As homeport to sixteen attack submarines and neighbor to a major submarine construction yard, General Dynamics' Electric Boat Corporation, all Officer and Enlisted submariners with the possible exception of nuclear trained Electronics Technicians (ETs), Electrician's Mates (EMs), and Machinist Mates (MMs), will be stationed at Groton for training, onboard an attack submarine or with a pre-commissioning crew for a new submarine. Enlisted sailors attending sub school will first go through Basic Enlisted Sub School (BESS), an 8 week program that teaches the rigors of undersea life. BESS includes training in patching leaks and ruptured pipes (shoring), firefighting, and boat handling techniques. After BESS, sailors will either go to a boat or to a follow on schools. Schools include BMS, AUXPAC, ATT, TCNO or to an A school, depending on their rating. The A Schools housed at NAVSUBASE NLON are SECF, SCERF, AUXPAC, TM "A". SECF is the combined "A" School for Sonar Technician Submarines(STS), Navigation Electronics Technician (ET NAV), and Firecontrol Technicians (FT). SCERF is the Submarine Communications Electronic Rating Field and it trains Communication Electronic Technicians (ET Comms) otherwise known as Radiomen. AUXPAC transforms new submariners into some of the finest mechanics in the U.S. Navy. TM "A" trains Torpedo's Mates (TM/MMW).
The main base occupies more than 687 acres (3 km²) plus over 530 acres (2 km²) of family housing, sixteen attack submarines, and the Navy's nuclear research deep submersible NR-1. The base also supports more than 70 tenant commands including, Commander Navy Region Northeast (CNRNE), Commander Submarine Group Two (CSG2), Naval Submarine School (NAVSUBSCOL), Naval Submarine Support Facility (NSSF), three Submarine Squadron staffs, and the housing and support facilities for more than 21,000 civilian workers, active-duty service members and their families.
On May 13, 2005, the Pentagon recommended that the base be closed. After review, the Base Realignment and Closure commission voted on August 24, 2005 to strike New London from the list of possible closures, thus allowing the base to remain open.