The war contributions of the Harvard Fatigue Laboratory in Cambridge, MA, were recorded in 169 Technical Reports, most of which were sent to the Office of the Quartermaster General. Earlier reports were sent to the National Research Council and the Office of Scientific Research and Development. Many of the reports from 1941 and later dealt with either physical fitness of soldiers or the energetic cost of military tasks in extreme heat and cold. New military emergency rations to be manufactured in large quantities were analyzed in the Fatigue Laboratory and then tested in the field. Newly designed cold weather clothing was tested in the cold chamber at -40 degrees Fahrenheit, and desired improvements were made and tested in the field by staff and soldiers in tents and sleeping bags. Electrically heated clothing was designed for high-altitude flight crews and tested both in laboratory chambers and field tests before being issued. This eyewitness account of the Harvard Fatigue Laboratory during World War II was recorded by Dr. G. Edgar Folk, who is likely the sole surviving member of that famous laboratory. ["The Harvard Fatigue Laboratory: Contributions to World War II" was written with Diana L. Thrift.] (Contains 4 figures.)