sentences:  World War II brought an additional with existing industrial buildings, as the arsenal produced steel artillery pieces.In 1959–1960, the Horace Hardy Lester Reactor was constructed on site, for material research programs, and operated there until 1970.In 1968 the Army ceased operations at the arsenal; were sold to the Watertown Redevelopment Authority, while the remaining were converted to the United States Army Materials and Mechanics Research Center (AMMRC), renamed the United States Army Materials Technology Laboratory (MTL) in 1985.