Japanese Zero Guns Synchronization ?

Hello,

Saw a picture and diagram of the WWII Japanese Naval Zero.

Apparently it had 2 machine guns in the upper cowling that fired thru the
prop.
True ?

My question regards the synchronization of these guns so they didn't hit the
prop.
How was this done ?
Mechanical interlock, electrical, or... ?

I'm an engineer, and wouldbe most appreciative for a technical description
of how it was accomplished.

Any pictures of the mechanism, etc. on the web ?

Thanks,
Bob