Leidos Undersea Systems Division (USD) is seeking a proactive and experienced Information System Security Engineer (ISSE) to serve as the subject matter expert for critical IT systems at Stennis Space Center, MS. The primary focus of this position is to design, develop, and implement secure information systems. The ISSE collaborates with engineers and developers to integrate robust security measures into systems, ensuring they are resilient against threats and vulnerabilities. This role requires a deep understanding of security engineering principles and a proactive approach to risk management throughout the system lifecycle. The successful candidate will be a self-starter, comfortable with extensive travel, and capable of thriving in dynamic and physically demanding environments. THE CHALLENGE (primary responsibilities) 37Perform and review technical security assessments to identify vulnerabilities and ensure compliance with information assurance (IA) standards and regulations.37 37Validate and verify system security requirements, establish system security designs, and integrate system security capabilities for various environments.37 37Build cybersecurity into systems deployed to operational environments, ensuring uniform application of security policies and enterprise solutions.37 37Assess and mitigate system security threats and risks throughout the program life cycle, contributing to security planning, assessment, risk analysis, and risk management.37 37Apply system security engineering expertise in areas such as system security design, life cycle, risk management, and security testing, using industry system security engineering methodologies.37 37Enforce the design and implementation of trusted relations among external systems and architectures and manage changes to systems while assessing security impact.37 37Support security authorization activities in accordance with Government regulations, Department of Defense and National Institute of Standards and Technology (NIST) Risk Management Framework (RMF) standards, and customer-specific information security policies, processes, and procedures.37 37Create, manage, and maintain all necessary documentation required to obtain and maintain a system's Authority to Operate (ATO). Ensure all evidence is accurately captured for ATO requests and extensions.37 37Identify, track, and manage all configuration changes. Implement and validate system security controls using Security Technical Implementation Guides (STIGs) and the Security Content Automation Protocol (SCAP) to ensure compliance.37 37Conduct field maintenance and system grooming to ensure optimal performance. Assist with installations and testing as needed.37 WHAT SETS YOU APART (basic qualifications) 37BS degree and 8 - 12 years of prior relevant experience3737Must have an active TS/SCI clearance.37 37Proven experience in a hybrid role combining system administration with information assurance.37 37Demonstrated experience as an ISSE/ISSM/ISSO/SCA.37 37Experience creating documentation to obtain and maintain an ATO.37 37Proficiency with STIGs and SCAP tools for configuration tracking and compliance.37 37Deep understanding of the Navy Risk Management Framework (RMF) process.37 37Comfortable working on multiple systems and components simultaneously in various configurations.37 37Holds one or more of the following certifications: Security+, CISSP, CISM, CAP, ISSEP.37 37Ability to work independently with minimal supervision.37 37Excellent communication skills, with the ability to translate complex IA concepts for various audiences.37 37Must be a US citizen.37 37Must possess a valid US passport and be willing to travel extensively.37 Work Environment & Physical Demands This role requires a significant commitment to travel and the ability to work in non-traditional office settings. The candidate must be able and willing to meet the following physical requirements: 37Extensive travel of up to 12 separate, week-long trips annually (approximately 6 OCONUS and 6 CONUS).37 37Requires movement around piers, docks, and industrial facility spaces. Ability to climb ladders up to 20 ft.37 37Required to transport or lift objects weighing up to 50 pounds.37 37Constant use of hands and fingers is required to operate tools and computer equipment.37 37Must be able to move about various workspaces, stoop, kneel, or reach for extended periods.37 37Able and willing to work aboard marine vessels of various sizes, which may include overnight stays.37 We are looking for a dedicated professional to join our Leidos team and make an immediate impact. If you are a skilled ISSE who is ready for a challenging and rewarding opportunity, we encourage you to apply. SUBSEAMSS Original Posting: June 4, 2026 For U.S. Positions: While subject to change based on business needs, Leidos reasonably anticipates that this job requisition will remain open for at least 3 days with an anticipated close date of no earlier than 3 days after the original posting date as listed above. Pay Range: Pay Range $107,900.00 - $195,050.00 The Leidos pay range for this job level is a general guideline only and not a guarantee of compensation or salary. Additional factors considered in extending an offer include (but are not limited to) responsibilities of the job, education, experience, knowledge, skills, and abilities, as well as internal equity, alignment with market data, applicable bargaining agreement (if any), or other law.