Day & Zimmermann is a privately held, family-owned diversified industrial services company founded in 1901 and headquartered in Philadelphia, Pennsylvania. The company operates across four primary business segments — Maintenance & Construction, Munitions, Government Services, and Workforce Solutions (Yoh) — and is one of the largest privately held U.S. corporations, reporting approximately $2.7 billion in revenue in 2023 with roughly 43,000–52,000 employees across approximately 150 global locations.
URL: Visit APIs.json URL
- Type: Index
- Position: Provider
- Access: 1st-Party
- x-type: company
- Ammunition, Architecture and Engineering, Construction, Defense, Engineering Services, Government Services, Industrial Services, Maintenance, Munitions, Nuclear Services, Power, Staffing, Workforce Solutions
- Created: 2026-05-22
- Modified: 2026-05-23
No public developer APIs have been published. Day & Zimmermann delivers its services through long-cycle service contracts, government-owned contractor-operated (GOCO) facilities, and direct client engagements rather than a programmable API surface.
- Founded: 1901 by Charles Day and Kern Dodge (originally "Dodge & Day"); John Zimmermann joined in 1907
- Ownership: Privately held; controlled by the Yoh family since the 1961 merger with the Yoh Company
- Chairman & CEO: Harold L. Yoh III
- Headquarters: Philadelphia, Pennsylvania
- Notable early work: Engineering on the Panama Canal's Gatun Lock System (1909)
Maintenance, construction, modification, and outage services for nuclear, fossil, and renewable power generation, plus chemical and industrial plants. Capabilities include welding, scaffolding, insulation, radiological protection, and turnkey plant services.
Ammunition manufacturing, loading, assembly, packing, storage, and demilitarization for the U.S. Department of Defense. Day & Zimmermann operates the Lake City Army Ammunition Plant in Independence, Missouri under a government-owned contractor-operated (GOCO) arrangement, producing small caliber ammunition (5.56mm, 7.62mm, .50 caliber) for the U.S. Army. Additional product lines include medium caliber rounds, warheads, fuzes, and direct/indirect fire munitions. The company is described as "one of America's leading producers of ammunition."
Integrated security services, explosive ordnance disposal (EOD), facility management, architecture, engineering, and commissioning for U.S. government agencies and federal installations. In 2011, Day & Zimmermann held 351 Army contracts valued at $151.8 million.
STEM staffing and talent placement operated through Yoh (yoh.com), a Day & Zimmermann company. Service lines include IT, engineering, life sciences, and healthcare staffing, along with RPO (Recruitment Process Outsourcing), MSP (Managed Service Provider), and EOR (Employer of Record) workforce models. Yoh maintains 6,000+ active contractors and 80+ years of STEM placement experience.
- Revenue: ~$2.7B (2023)
- Employees: ~43,000–52,000
- Locations: ~150 global
- Recognition: Engineering News-Record Top 500 Design Firms
- Lake City Army Ammunition Plant — Independence, Missouri (operator, GOCO; small caliber ammunition for the U.S. Army)
- Corporate Headquarters — Philadelphia, Pennsylvania
- Yoh — STEM staffing and workforce solutions
- Day & Zimmermann NPS — Nuclear power services division
- SOC LLC — Government security services
U.S. Army, U.S. Department of Defense, U.S. Department of Energy, NRC-licensed utilities, investor-owned utilities, chemical and petrochemical operators, and federal civilian agencies.
- Website
- About
- Leadership
- Maintenance and Construction
- Munitions
- Government Services
- Workforce Solutions (Yoh)
- Careers
- News and Events
- Wikipedia
- No public developer APIs (REST, GraphQL, gRPC, etc.)
- No OpenAPI, AsyncAPI, or JSON Schema specifications
- No GitHub organization
- No SDKs, CLIs, or developer tooling
- No public pricing, rate limits, or FinOps surface
- No public RSS/Atom feed or changelog
- No developer portal, sandbox, or API console
- Kin Lane - kin@apievangelist.com