a gyrocompass and repaired equipment in preparation for final acceptance trials on 7 March. Although successfully put through her paces, the boat returned to the yard for further alterations, including the installation of new diving rudders. Trouble with the Sperry gyrocompass rudder control mechanism — as well as continued modifications to engines and other machinery — kept the boat in the New York Navy Yard through the end of the year. Finally tested at sea in February 1917, the gyro stabilizer and diving rudders then failed in heavy weather. After G-4 returned to the yard, the broken rudders were repaired and the stabilizer mechanism removed by 10 March. Sailing to New London on 24 April, G-4 was attached to Division Three, Submarine Flotilla. For the next year, she combined experimental work with new sound detection devices with training new student crews in submarine operations and torpedo firing, a period of time punctuated by her joining the submarine tender for harbor submarine net defense experiments. Later in the month, G-4 carried out sound experiments with and in the Thames River and in Long Island Sound. In late July, she conducted battle exercises and submerged attack drills against SC-6. On 22 October, Thetis experimented with sound and magnetic detectors while G-4 lay on the bottom of Long Island Sound. Over the winter, she conducted numerous sound experiments with the newly established Submarine School in the area of Block Island Sound and Long Island Sound. In March 1918, G-4 shifted from New London to Newport, where she conducted magnetic detector experiments with . The submarine also conducted practice approaches and torpedo instruction for officer and enlisted submarine students. On 21 May, G-4 commenced test firing the new Mark VII torpedo for installation in O and N-class submarines, evolutions that lasted through mid-July. The boat then returned to New London for a yard period, undergoing motor and electrical repairs through October. Although G-4 resumed training and instruction duties on 4 November, the boat was slated for inactivation on 24 February 1919. G-4 continued her training and experimental duties until 1 March, when she was placed in ordinary for stripping and inactivation. She decommissioned on 5 September, was designated as a target for depth charge and ordnance tests on 6 December, and was sold for scrapping to Connecticut Iron and Metal Company of New London on 15 April 1920. She was struck from the Naval