Today's "Tokyo Rose" subject

“Purple” was a cipher machine used by Japanese diplomats, not the military.

The US exploited JN-25, a Japanese fleet code, to discover Yamamoto’s travel plans
and ambush him.

Gary (NSA retiree)

This column?

How did WWII propaganda broadcaster Tokyo Rose get info on Allied ship movements?

in reply to the comment at the end

From the column:

"Iva Toguri and her associates gathered much of the news they broadcast listening to short-wave radio from the U.S. mainland. In that respect, we did “leak information like a sieve.”

Probably the worst example was the “May incident”, where Congressman Andrew May told a press conference that the Japanese were setting their depth charges too shallow and allowing U.S. subs to avoid them (and numerous media sources were stupid enough to pass along his comments). The Japanese Navy subsequently developed depth charges that exploded deep enough to sink up to ten U.S. submarines.