Day & Zimmermann offers services as distinct as day and night. Its companies provide engineering, construction, and plant maintenance; staffing; munitions manufacturing and demilitarization; defense solutions, and various government services. A top global contractor, Day & Zimmermann offers operations, contract support, and maintenance services to US and foreign governments, as well as commercial customers. Its Day & Zimmermann NPS unit maintains half of nuclear plants in the US. Staffing subsidiary Yoh Services specializes in filling IT, engineering, and health care positions. Founded in 1901, Day & Zimmermann is owned and managed by the Yoh family, which has headed the firm for three generations.