Hallam Evans Mendenhall joined the BTL's Research Department in 1928, and retired after a 36-year Bell System career. During the first 22 years, he specialized in research and development of all types of vacuum tubes. During the war, he worked with WECo on the manufacture of electron tubes and then returned to the Bell Labs' Research Dept. During his career he was granted 13 patents on vacuum tube devices and processes, and he was the author of several technical papers on those subjects.