Accounts Payable; AP) Specialist No No department On-Site

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 '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.

We are seeking an experienced Accounts Payable (AP) Specialist to join our growing accounting team. This will be the second AP Specialist on the team and will directly support our Senior Accounting Manager. The AP Specialist will be responsible for ensuring accurate and timely processing of vendor invoices, payments, and employee expense reports. The ideal candidate is detail-oriented, organized, and thrives in a fast-paced, dynamic environment where accuracy and accountability are critical.

• Review, code, and process vendor invoices in compliance with company policies and procedures.
• Manage the AP inbox and vendor communications, ensuring timely responses.
• Assist with the three-way matching process (PO, receipt, and invoice) and resolve discrepancies.
• Partner with Supply Chain and Engineering departments to reconcile item receipts, including quantities and prices, between procurement and expense management platforms.
• Confirm vendor payment details and process check runs, ACH payments, and wire transfers to ensure timely payment of invoices.
• Reconcile vendor statements and follow up on outstanding balances.
• Ensure compliance with internal controls and audit requirements.
• Support monthly, quarterly, and year-end close activities, including AP accruals.
• Manage the employee corporate card program, including processing monthly expense reports, employee reimbursements, and corporate credit card reconciliations.
• Provide ad hoc support to the Senior Accounting Manager as needed.

• 3+ years of accounts payable experience, preferably in manufacturing, aerospace, or defense.
• Strong understanding of GAAP and accounting processes related to AP.
• Proficiency with ERP systems (Net Suite experience preferred), expense management platforms (Ramp), procurement platforms (Silkline), and Excel.
• Exceptional attention to detail, accuracy, and organizational skills.
• Strong communication and problem-solving abilities.
• Ability to thrive in a fast-paced, hands-on environment and meet tight deadlines.
• U.S. Person status required due to government program requirements.

All employees are granted long-term stock incentives as part of their employment as Castelion. All employees receive access to comprehensive medical, vision, and dental insurance, and the company offers four weeks of paid time off per year.

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.

A successful candidate will have a genuine passion for Castelion's mission and consistently look for ways to contribute to the company's technical goals and prevent hardware blockers. Ability to work in a fast paced, autonomously driven, and demanding atmosphere. Strong sense of accountability and integrity.

Proactively communicates blockers. Trusted in previous roles to be voice of company with regulators, suppliers, gate keepers and customers. Capable of tactfully managing relationships with stakeholders to achieve company-desired…