Day & Zimmermann

Day & Zimmermann is a privately held, family-owned company that has quietly become one of the Pentagon's more important munitions suppliers, alongside a security and staffing business most people never connect to the same name. Founded in Philadelphia in 1901 as Dodge & Day, the firm added munitions and engineering work under later generations of the Yoh family, who still control it today, and it now operates from roughly 150 locations with about 43,000 employees. Its munitions business is the core of its defense identity. Through American Ordnance, a joint venture Day & Zimmermann operates, the company manufactures artillery and tank ammunition for the U.S. military and approved foreign buyers, running the government-owned Iowa Army Ammunition Plant and the storage and demilitarization operations at the Milan Army Ammunition Plant in Tennessee. That work spans legacy shell types still in NATO stockpiles through newer fuzing, safe and arm devices, and ignition safety technology, and it has taken on new urgency as the U.S. and its allies work to rebuild artillery shell stocks depleted by the war in Ukraine.

Day & Zimmermann has appeared repeatedly in trade press rankings of top defense manufacturers largely on the strength of this ammunition production. A separate Government Services business runs the installations that make that manufacturing possible, and a good deal more. It designs and builds military facilities, operates and maintains ammunition plants beyond the ones it owns outright, and provides base operations support covering vehicle and equipment maintenance, supply services, explosive ordnance storage, and transportation management at posts in the U.S. and overseas. A security services line, built around the company's SOC subsidiary, provides armed protective services at military installations, government facilities, and diplomatic posts around the world, work distinct from but adjacent to the ammunition and construction businesses. Outside defense, Day & Zimmermann's civilian businesses round out the group.

Yoh Services provides staffing and workforce solutions across multiple industries, tracing back to the 1961 merger that brought the Yoh name into the company. An engineering and construction arm handles large industrial projects including power plant work, a lineage that runs back to some of the firm's earliest twentieth century contracts, including work on the Panama Canal's lock system. Because Day & Zimmermann is privately held, detailed financials are not public, but Forbes has repeatedly counted it among the largest privately held companies in the United States, and trade press has ranked it among the larger defense contractors globally, evidence of how much of its revenue now runs through the ammunition and government services businesses rather than its older commercial staffing roots.