Electric Boat acquired a license to manufacture MAN diesels, probably in 1909. These were initially manufactured by the Fore River Shipyard of Quincy, Massachusetts, where most of Electric Boat's early submarines were built under subcontract. NELSECO was established in Groton to take over diesel manufacturing from Fore River when difficulties were encountered, finishing the work on engines begun by Fore River. It was a subsidiary of the Electric Boat Company for its entire existence. The E- and F-class submarines, launched 1911-12, were initially equipped with these diesels; they were replaced in 1915 as NELSECO's initial efforts were unsatisfactory. The company was incorporated on 11 October 1910, with production starting in July 1911. The company built the engine for first Diesel powered yacht in America, Idealia, built during 1911 and launched by ELCO in 1912. Idelia was owned by ELCO into 1916 and used for demonstrating the application of Diesel engines in yachts. On 22 October 1913 under ELCO corporate manager Henry R. Sutphen Idealia performed a trial on the Hudson River witnessed by naval engineers and architects on a run of about sixty miles from the Columbia Yacht Club at 86th Street to Croton Point and back. The original Idealia installation was a reversible, air started, two cycle engine with six working cylinders and one two stage air compression cylinder that was rated at 150 horsepower at 550 revolutions per minute. The original two stroke engine was replaced by a NELSECO 120 horsepower four cycle engine by February 1915. The company was probably disestablished around 1925, as the last United States S-class submarine was completed in that year, and no subsequent US submarines were equipped with NELSECO engines. Electric Boat had a drought in submarine contracts 1918-1931, which probably caused NELSECO's demise.
Nelseco Navigation Company operates ferry service to Block Island in Rhode Island. At least two ferries have been named NELSECO. One was launched in 1917 and scrapped circa 1972 and the other was launched in 1981 and scrapped circa 2010.
