Stig / Ed. I don't know whether it's fact or fiction but certainly US Intellgence published a report on a Japanese Naval POW who described it (but rather vague using phrases like "possibly" or "not known") (first link); at the bottom of the other link is a drawing presumably by the POW of a launch site.
No doubt if a few B-29s had actually been shot down, the authorities would have taken it more seriously.......
Regards
Nick
https://dl.ndl.go.jp/info:ndljp/pid/...1506&__lang=en
https://forum.axishistory.com/viewtopic.php?t=236157