Ann Pfau notes that there is a vast descrepancy between what soldiers said they heard (and sometimes wrote home about) and what was recorded/transcribed from the Zero Hour broadcasts and she (and I) suspect that the soldiers' testimony should get more weight than it is currently fashionable to give them.
That first link gives the history of several different Japanese propaganda campaigns, of which "Zero Hour," aimed at American servicemen, is the most famous. It began in March 1942. POWs were invited to help participate (with a warning that their safety couldn't be assured otherwise). They apparently attempted to somewhat defang the propaganda, which had to be sandwiched in with entertainment. First 20 minutes, then 45 minutes, then 75 minutes: "5 minutes of prisoner messages read by Cousens and the fifteen to twenty minute "Orphan Ann" spot, a light music spot for which Iva was the DJ, and read a script prepared for her by Cousens. The "American Home Front News" which followed, was written by Japanese and read by Ince. It was given a five- to ten-minute slot, but frequently there was not enough material to fill the slot and it ended with more light music records."
There were plenty of grievances for the Japanese to try to exploit: India vs Britain, blacks in America, and old American vs British attitudes--and they tried to take advantage of them all. It isn't obvious that they had much luck in the US. On the other hand, every little bit helps.