transited the familiar waters of Long Island Sound before arriving at the mouth of the East River on 22 June. While standing down the river with , however, the two boats collided with submarine K-22 in an unusual three-boat accident. Fortunately, none of the boats suffered any damage. G-2 entered the Navy Yard there for an extended overhaul later that day. Escorted to Provincetown, Massachusetts, by Ozark and tug , G-2 commenced final acceptance trials from 1–10 December. Following those successful evolutions, during which the Trial Board noted numerous items requiring modernization, the boat moved back to New York for an overhaul on 14 January 1916. Six months later, G-2 shifted to the Lake Torpedo Boat Company yard for completion, receiving new diving rudder gear, hydroplanes, electrical wiring and a new crankshaft. This yard work required extensive alterations and the boat did not return to service until convoyed to New London, Connecticut, by on 28 June 1917. On 21 August, G-2 sailed to Boston, Massachusetts via the Cape Cod Canal to operate with the destroyer , submarine chaser SC-6, and steam yacht . There, the boat helped a Navy Experimental Board embarked in Margaret carry out various sound detector tests in nearby waters. The submarine also conducted practice approaches and served as an instruction platform for officer and enlisted submarine students. Shifting back to New London on 20 October, G-2 combined work on sound detection devices with training for the newly established Submarine School off Block Island and in Long Island Sound. During seven months of operations, she experimented with magnetic detectors and dragging devices and tried out new periscopes and other submarine equipment. The boat carried out these tests with section patrol boats and , as well as numerous subchasers. Learning of the possible proximity of German U-boats, she conducted four-day patrols off Block Island in late June 1918 and again in mid-July. G-2 continued schoolship duty out of New London through the end of World War I, testing listening and flare signaling devices (including the Very System Signal) among other pieces of equipment. On 30 August, for example, her crew tested the strength of the pressure hull, and the reliability of electric equipment, against depth charge explosions. On 12 September, Thetis experimented with a magnetic detector while G-2 lay on the bottom in of water and, in November, G-2 even conducted experimental work with patrol seaplanes. This duty