After receiving a Ph.D. in mathematics from Yale, she began her professional life as a math teacher at Vassar College, her alma mater, where she ultimately became an associate professor. Later, she worked as a top scientist at Sperry Corporation and its predecessors.
However, her employer of choice was always the Navy, which she joined in 1943 at the height of World War II. As a lieutenant assigned to the Bureau of Ordnance Computation Project at Harvard University, Admiral Hopper was thrust into the world of computing as a programmer on the first large scale digital computer, the Mark I.
Mustered out of the Navy in 1946, she remained at Harvard as a faculty member in the computation laboratory. She continued to work on Mark I and Mark II Navy computers and maintained her Navy career as an active duty reservist.
Although retired from the Navy reserve in 1966 because of age, Admiral Hopper was recalled within a year to full-time active duty and steadily advanced to flag rank. Her assignment to the Naval Data Automation Command in Washington, D.C., permitted her to refine computer language techniques to the Navy's advantage and to keep that service at the cutting edge of computer technology.