New London Ship and Engine Company
Early twentieth-century American manufacturer of diesel engines for submarines, yachts, and other marine applications.
Last updated August 25, 2026
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Overview
New London Ship and Engine Company, commonly abbreviated NELSECO, was an American marine-engine manufacturer established at Groton, Connecticut, as a subsidiary of the Electric Boat Company. Its principal purpose was to produce diesel engines for Electric Boat's submarines after the parent company obtained a license to manufacture engines based on designs from the German firm Maschinenfabrik Augsburg-Nürnberg, commonly known as MAN. Electric Boat initially arranged for the Fore River Shipyard in Quincy, Massachusetts, to manufacture the licensed engines. Fore River was also building many of Electric Boat's early submarines under subcontract, but difficulties in engine production led Electric Boat to establish NELSECO and move the work to Groton. The company was incorporated on October 11, 1910, and began production in July 1911. Its early engines were installed in the E-class and F-class submarines, launched in 1911 and 1912. These initial installations were not considered satisfactory and were replaced in 1915, an episode that illustrates the technical challenges involved in adapting large diesel machinery for early submarine service. NELSECO also participated in the broader development of diesel propulsion for civilian craft. It supplied the engine for Idealia, a yacht launched by Electric Launch Company, or Elco, in 1912. Idealia was retained by Elco as a demonstrator until 1916 and helped publicize the potential of diesel propulsion in yachts. The original installation was a reversible, air-started, two-stroke engine with six working cylinders and a two-stage air-compression cylinder. It was rated at 150 horsepower at 550 revolutions per minute. By February 1915, the original engine had been replaced by a NELSECO four-stroke engine rated at 120 horsepower. The company remained an Electric Boat subsidiary throughout its existence and was closely tied to the parent's submarine-construction program. Its engines were used in a number of early United States submarines, including boats associated with the S-class program. NELSECO appears to have ceased operations or been disestablished around 1925. The likely timing corresponds with the completion of the last United States S-class submarine and the absence of later American submarines equipped with NELSECO engines. Electric Boat subsequently experienced a prolonged shortage of submarine contracts between 1918 and 1931, a commercial condition that likely contributed to the end of the engine subsidiary. NELSECO should not be confused with the later Nelseco Navigation Company, also known as Interstate Navigation Company, a ferry operator serving Block Island. That company used the NELSECO name on vessels, including ferries launched in 1917 and 1981, but it was a separate maritime enterprise rather than a continuation of the engine manufacturer. NELSECO's historical importance lies in its role in the early American adoption of diesel propulsion, particularly the effort to develop dependable diesel machinery for the United States submarine fleet.
History
Electric Boat obtained a license to manufacture MAN diesel engines around 1909. The first licensed engines were produced by the Fore River Shipyard in Quincy, Massachusetts, which was also involved in the construction of Electric Boat's early submarines. Manufacturing difficulties prompted Electric Boat to establish the New London Ship and Engine Company at Groton, Connecticut, to assume responsibility for diesel production and complete engines already begun at Fore River. NELSECO was incorporated on October 11, 1910, and started production in July 1911. Its first major application was submarine propulsion. The E-class and F-class submarines launched in 1911–1912 initially received NELSECO engines, but those engines were replaced in 1915 after the original installations proved unsatisfactory. The episode reflects the experimental nature of submarine diesel technology during this period, when manufacturers were still adapting stationary and marine-engine concepts to the demanding requirements of underwater vessels. The company also pursued civilian marine applications. Electric Launch Company, commonly called Elco, launched the yacht Idealia in 1912 with a NELSECO diesel engine. Elco used the yacht as a demonstrator through 1916. The original propulsion system was a reversible, air-started, two-stroke engine with six working cylinders and a two-stage air-compression cylinder, rated at 150 horsepower at 550 rpm. By February 1915, this engine had been replaced with a NELSECO four-stroke unit producing 120 horsepower. NELSECO was an Electric Boat subsidiary throughout its existence. Its fortunes were therefore closely connected to Electric Boat's submarine orders. The company probably disappeared around 1925, when the final United States S-class submarine was completed and later American submarines no longer used NELSECO engines. Electric Boat's lack of submarine contracts from 1918 to 1931 likely weakened the commercial basis for maintaining a dedicated engine subsidiary. The NELSECO name later appeared in connection with Nelseco Navigation Company, also known as Interstate Navigation Company, a separate ferry operator serving Block Island. Ferries bearing the name were launched in 1917 and 1981. Those vessels represent later maritime use of the name and should not be treated as products or corporate successors of the original New London Ship and Engine Company.
- 1925
Likely end of operations
[1]The company was probably disestablished around the time the last United States S-class submarine was completed; the exact closure date is not established.
- 1915
Initial submarine engines replaced
[1]The original NELSECO engines in E- and F-class submarines were replaced after unsatisfactory results.
- 1912
Idealia launched with NELSECO propulsion
[1]The Elco yacht Idealia entered service with a NELSECO diesel engine and became a demonstrator for yacht diesel propulsion.
- 1911
Production begins
[1]NELSECO began producing marine diesel engines in July 1911 after taking over work from Fore River Shipyard.
- 1911
First submarine applications
[1]NELSECO diesels were installed in early E-class and F-class United States submarines.
- 1910
Company incorporated in Groton
[1]The New London Ship and Engine Company was incorporated on October 11, 1910, as an Electric Boat subsidiary.
- 1909
Electric Boat obtains a MAN diesel manufacturing license
[1]Electric Boat acquired authorization to manufacture MAN diesel engines, establishing the technical basis for its subsequent marine-engine program.
Products and positioning
Specialist marine-engine manufacturer serving Electric Boat's early submarine program and experimenting with diesel propulsion for civilian craft.
Submarine propulsion · 1911
NELSECO submarine diesel engines
Diesel engines manufactured for Electric Boat's early submarine program under a license based on MAN designs. Initial examples were installed in E-class and F-class submarines launched in 1911–1912, although those installations were replaced in 1915 after proving unsatisfactory. NELSECO engines were also associated with later early United States submarine construction, including the S-class period.
Yacht propulsion · 1912
Idealia diesel installation
A NELSECO marine diesel installation supplied for Idealia, an Elco yacht launched in 1912 and used as a demonstrator for diesel propulsion in yachts. The original system was a reversible, air-started, two-stroke engine with six working cylinders and a two-stage air-compression cylinder, rated at 150 horsepower at 550 rpm. It was replaced by a 120-horsepower four-stroke NELSECO engine by February 1915.
Brand decisions
1915
Replace early submarine diesel installationsGeneration changeBackground
The first NELSECO engines installed in E-class and F-class submarines were judged unsatisfactory in service.
Action taken
The original engines were replaced in 1915.
Aftermath
The replacement decision limited the success of NELSECO's initial submarine-engine installations, although the company continued supplying marine engines afterward.
1915
Upgrade Idealia's propulsion systemGeneration changeBackground
Elco used Idealia to demonstrate diesel propulsion for yachts, creating an opportunity to evaluate the initial NELSECO installation.
Action taken
The original 150-horsepower two-stroke engine was replaced by a NELSECO four-stroke engine rated at 120 horsepower by February 1915.
Aftermath
The yacht continued serving as a practical demonstration of diesel propulsion under a revised NELSECO configuration.
1910
Create a dedicated diesel-engine subsidiaryStrategyBackground
Electric Boat needed a more reliable manufacturing arrangement after difficulties arose while Fore River Shipyard was producing licensed MAN diesels.
Action taken
Electric Boat incorporated NELSECO at Groton to take over diesel-engine production and finish engines already begun at Fore River.
Aftermath
The subsidiary became Electric Boat's dedicated marine-engine manufacturing arm and supplied engines for submarines and civilian vessels.
Recent events
- 1915
Early submarine diesel installations replaced[1]
Product generation · Other
The initial NELSECO diesel installations in E- and F-class submarines were replaced after performance and suitability problems.
- 1912
NELSECO engine powers the yacht Idealia[1]
Product launch
NELSECO supplied the engine for Idealia, an Elco yacht used to demonstrate diesel propulsion for civilian boating.
- 1911
NELSECO begins marine-engine production[1]
Product launch
Production began in July 1911 as the company took over diesel-engine work previously conducted for Electric Boat by the Fore River Shipyard.
- 1910
New London Ship and Engine Company incorporated[1]
Other
Electric Boat established its Groton-based diesel-engine subsidiary, formally incorporated on October 11, 1910.
Sources1 sources
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