Watertown Arsenal, Building No. 100, Wooley Avenue, Watertown, Middlesex County, MA

Significance: Building No. 100, the Horace Hardy Lester Reactor, was the first nuclear reactor designed to meet the needs of the U.S. Army materials research programs. It continued a long history of nondestructive materials testing at Watertown Arsenal, including the Emery Testing Machine of 1879 and a 280,000-volt x-ray machine for materials radiography in 1922, and reflected Watertown Arsenal's emphasis on materials testing after World War II. At the time of construction, its "segregational" design, which allowed several discrete experiments to be conducted simultaneously, was unique.
Survey number: HAER MA-20-R