Thales Defense & Security, Inc. (TDSI) is seeking a Principal Systems Engineer for its Aurora, IL office. This position provides Technical Leadership on Helmet Mounted Display (HMD) design activities, including bids, requirements decomposition and flow down, verification, testing, and troubleshooting. The candidate will work as part of a design team that includes Systems, Software, Electrical, Mechanical, and Field Service engineers. The role requires direct interaction with customers and support for Business Development in early business capture phases. Extensive knowledge of head and helmet mounted display systems is essential.