Robert "Mac" McNelis joined NSA in 1964 as a math intern. Upon graduation from the intern program in 1967, he spent the rest of his career in the COMSEC organization. There, Mac became a leader in moving the directorate to more math-based procedures.

Responding to the "technical revolution" of the 1970s and 1980s, Mr. McNelis developed a science of system evaluation, now recognized as a "huge culture shift" in COMSEC practices. He directed a large staff in redesigning mathematical applications for crypto-security, and instituted a documentation program to improve evaluation quality. From 1984-1995 as Chief Evaluation Scientist, he was principal author of the Functional Security Requirements Specification document, which influenced the design and development of all U.S. government cryptographic devices.

In the same period, he developed measurable evaluation standards for security systems. When the COMSEC organization developed a requirements catalog of over 2,500 items, each based on an identified vulnerability in equipment, Mr. McNelis personally vetted each requirement. When the U.S. and UK discussed standards, he drove all significant change on the U.S. side during his tenure.

For thirty years, Mr. McNelis taught new crypto-mathematicians the fundamentals of system security. Known as an exacting taskmaster, he raised generations of Information Assurance Directorate technical personnel to work at the highest standards.

"Mac" built a critical field for the Information Assurance mission, and influenced two generations of NSA IAD analysts.