Havok formerly wore an anti-grav harness for flight and a containment suit that monitored his energy output. As a member of the Australian X-Men, Havok was once rendered invisible to all forms of electronic detection. He became Havok in X-Men (1st series) #58.
Mutant X was actually only the title of the book, it was never used as a codename for Alex inside the issues. He was constantly refered to as Havok.