Senior Human Resources Generalist

About Castelion

Castelion is bringing a new approach to defense development and production: one that focuses on short, iterative design cycles, rapid testing in development, and modern commercial manufacturing strategies for production at scale. We're designing, building, and testing next generation long range strike weapons systems to give America and its Allies a definitive edge and deter future conflicts.

Senior Human Resources Generalist

The Sr. Human Resources Generalist will lay a foundational role in building and optimizing the core people infrastructure that enables our teams to do their best work—on the ground and beyond.

You'll design, implement, and continuously improve critical HR systems and processes across onboarding, payroll, benefits administration, and people analytics. Partnering closely with leadership and cross-functional teams, you'll help create scalable, compliant, and employee-centric experiences that support rapid hiring and operational complexity.

Responsibilities

Payroll Operations

• Deliver 100% on-time payroll processing with little to no error rate.
• Serve as first point of contact for payroll tax inquiries, notices, and agency communications.
• Ensure timely and accurate payroll tax filings, reconciliations, and reporting across federal, state, and local jurisdictions, meeting all deadlines to avoid penalties.
• Resolve payroll discrepancies and inquiries within 24–48 hours.
• Ensure compliance with multi-state wage and hour laws, tax regulations, and reporting requirements.
• Continuously improve payroll processes to support rapid scaling through automation and system optimization.

Benefits Administration

• Manage and optimize employee benefits programs (e.g., retirement, leave management, health insurance) to increase employee participation and satisfaction.
• Respond to benefits inquiries within 24 hours with 95% resolution satisfaction.
• Support open enrollment and serve as a trusted resource for employee questions.
• Analyze utilization trends and recommend benefit enhancements.

People Analytics & HR Systems

• Maintain HRIS integrity and ensure accurate, real-time employee data.
• Translate data into actionable insights for leadership and workforce planning.
• Support compliance reporting and audits with a high degree of accuracy.

Onboarding

• Ensure Day 1 readiness for all new hires (e.g., new hire documentation, new hire checklist, compliance requirements).
• Maintain 95% new hire satisfaction score on onboarding surveys.
• Track onboarding progress and identify opportunities to enhance efficiency and engagement.

General HR Operations

• Support onboarding and offboarding with a seamless, high-quality experience.
• Respond to employee inquiries within 24 hours, with 90% first-touch resolution rate.
• Maintain audit-ready employee records with compliance-free deficiencies.
• Ensure completion of offboarding tasks within company standards.
• Identify opportunities to automate, streamline, and strengthen HR processes.

Basic Qualifications

• Bachelor's degree in Human Resources, Business, or related field
• 3+ years of HR experience with strong ownership of payroll and benefits
• Experience working in a startup or high-growth environment
• Proficiency with HRIS platforms (e.g., Rippling, ADP, Workday, or similar)
• Strong analytical skills (excel required; dashboards/BI tools a plus)
• High attention to detail and ability to manage sensitive information
• Solid understanding of employment laws and compliance requirements

Preferred Skills and Experience

• Experience in aerospace, defense, manufacturing, or other regulated industries
• Familiarity with government compliance environments (e.g., audits, reporting standards)
• Experience building or scaling HR processes from the ground up
• HR certification (PHR, SHRM-CP, or equivalent)
• Payroll certification (CPP or equivalent)

Leadership Qualities

Bias to Action and Creative Problem Solving. Desire and experience questioning assumptions in ways that lead to break through ideas that are ultimately implemented. Successfully bring in applicable processes/concepts/materials from other industries to achieve efficiency gains. Ability to personally resolve minor issues in development without requiring significant support.

High Commitment, High Initiative. A succes