[2] Nygren served as damage control officer aboard the destroyer USS Hughes (DD-410) in 1946 as she was prepared for use as a target in the Operation Crossroads atomic bomb tests at Bikini Atoll later that year.

He then returned to Seattle, where he was assigned to the Submarine Battalion of the Organized Reserve while he spent a year pursuing a Bachelor of Science degree in mechanical engineering at the University of Washington.

[1][2][4] Leaving the Naval Reserve, Nygren began his career in the United States Coast and Geodetic Survey in September 1947 as a civilian deck officer.

As a lieutenant (junior grade), Nygren used this newfound knowledge to serve as a maritime pilot for a convoy of United States Navy tank landing ships (LSTs) as it voyaged along the Alaska North Slope.

[5] In 1954, Nygren left Pathfinder for over three years of duty as head of a Coast and Geodetic Survey Division of Geodesy field party measuring the acceleration of gravity.

The project took him to the Midwestern United States for work similar to geophysical surveys and elsewhere in the world to establish gravity base stations.

[1][4][5] During his time on the planning staff, he was involved in many of the negotiations that led to the creation of a new United States Government scientific organization, the Environmental Science Services Administration (ESSA).

In 1968, Nygren became the commanding officer of Surveyor while she was operating in Cook Inlet, and with him in command, she conducted pioneering geophysical surveys of gravity and magnetism – prototypes for future studies of the continental shelf – between Hawaii and the United States West Coast before returning to the Bering Sea, where she conducted operations as far north as Cape Prince of Wales.

His duties took him on visits to Alaska, Antarctica, the International Hydrographic Bureau in Monaco, and the World Meteorological Organization in Geneva, Switzerland.

[6] He also directed the expansion of the NOAA Corps training program and arranged for it to be located at the United States Merchant Marine Academy in Kings Point, New York.

[10] [7] The program for the award ceremony cited his achievements as follows: Rear Admiral Nygren has provided distinguished direction to the NOAA Corps through outstanding professional competence and leadership.

His highly effective guidance, insight, and management are directly responsible for the necessary expansion, development, and adaptation of the Corps to best serve the public interest and to support the diverse missions of the National Oceanic and Atmospheric Administration (NOAA) and the Department.

He was mostly responsible for the expansion of the NOAA Corps training program and for its location at the United States Merchant Marine Academy, Kings Point, New York.

Rear Admiral Nygren has given special attention to the concerns of minority groups, including the commissioning of women into the Corps to serve in the field on an equal basis with men.