Hamann attended Bellarmine College Preparatory and was a football player at Santa Clara University.^[1] After graduating in 1932, he served as the university's alumni association director before joining the United States Navy during World War II. After the war, Hamann left the Navy as a Lieutenant Commander, to become a division manager for General Motors.

On March 10, 1950, Hamann was appointed city manager of San Jose by a 4–3 vote of the city council. His first large project was to pass a bond measure to upgrade and expand the city's sewage system, building a new sewage treatment plant near Alviso. At the time, the city's sewage system was insufficient to handle the large amount of waste produced by the local canneries; Hamann's new plant was designed not just for current demand, but allowed for a significant expansion.

Hamann then directed an aggressive growth program for the city. Growing up in Orange County, Hamann felt that the development of that area, consisting of several mid-sized cities without a dominant city in the region, was a failure and worked to ensure that San Jose became the major city of the Santa Clara Valley. Central to this project were "strip annexations"—Hamann and his staff would determine where new tax-generating developments such as shopping centers were likely to be built, and would annex small strips of territory around the property to ensure no other city could claim the property so that San Jose would receive the sales tax revenue produced by property when it was finally developed.

When industries decided to move into or expand in the area, Hamann would ensure they found a willing partner in the city. IBM wanted to move its research staff out of downtown to a dedicated facility to be sited on unincorporated land south of San Jose, but were being blocked by the Santa Clara County Board of Supervisors. Hamann simply had San Jose annex the proposed site and pushed the project's approval through the city council.

In addition to annexing unincorporated territory, Hamann's staff also annexed existing neighborhoods, including Cambrian Park, and one city. When the city of Alviso attempted to annex the new sewage plant to boost tax revenue, Hamann countered by having San Jose annex Alviso. A special city staff, known as Dutch's Panzer Division, executed 1377 annexations during his time in office—previous to Hamann's administration there had been a total of 42.

In 1969, anti-growth candidates were elected to the city council, and Hamann chose to resign rather than work with a city council opposed to his program. He returned to Santa Clara University as its vice president of development. He was inducted to the SCU sports Hall of Fame. Hamann and his wife Frances died on Pan Am Flight 1736 on March 27, 1977, in the Tenerife airport disaster, a collision of two Boeing 747s in the Canary Islands. This incident remains the worst aviation accident in history.

• List of city managers of San Jose, California

• McKay, Leonard (2006). "Dutch Hamann — Part One". San Jose Inside. Retrieved March 11, 2006.
• McKay, Leonard (2006). "Dutch Hamann — Part Two". San Jose Inside. Retrieved March 11, 2006.
• Rogers, Paul (1999). "Hamann: San Jose's growth guru". San Jose Mercury News. Archived from the original on February 23, 2005. Retrieved March 6, 2005.
• Trounstine, Philip J.; Terry Christensen (1982). "Flashback: a short political history of San Jose". Political Science Department, San Jose State University. Archived from the original on March 13, 2001. Retrieved March 11, 2006.

• City of San Jose
• Santa Clara University