But by 1945 the cavity magnetron was documented to
some extent (probably
enough to make one if you understood Maxwell's Equations ;-)) in the ARRL
handbook. FWIW, this book was published _before_ the war ended.
That is because the Japanese and Germans had them - no longer a
secret. The Japanese actually were quite far advanced in the art of the
magnetron.
For that matter, SCR-268 radars (first generation U.S. searchlight and
gun control radars) were being sold as surplu before the war ended, too.
William Donzelli
aw288(a)osfn.org