Microwave (1 mm - 1 m, 300 MHz - 300 GHz)

radar. As an example, 1965 Nobel Prize in Physics laureate Julian Schwinger did some notable work in the area in World War II, while most other physicists went to the Manhattan Project instead.

This is well highlighted in QED and the men who made itby Silvan Schweber (1994). Designing the cavity wasn't easy. One of the key initial experiments of quantum electrodynamics, the Lamb-Retherford experiment from 1947, fundamental for modern physics, was a direct consequence of post-radar research by physicists who started to apply wartime developments to their scientific search.

Wikipedia also mentions en.wikipedia.org/w/index.php?title=Microwave&oldid=1093188913#Radar_2:

The first modern silicon and germanium diodes were developed as microwave detectors in the 1930s, and the principles of semiconductor physics learned during their development led to semiconductor electronics after the war.