Thousands of tons of bombs were dropped on Japan in WW2. Many of them didn't explode. This airport was apparently an active airfield at the time the US was bombing Japan and 500lb bombs were the sort of thing used to destroy parked planes.
Yes, someone could have snuck into an airport and buried a bomb underneath the runway, then cleaned up the digging operation so as to not be noticed, but horses, not zebras.
Yes, someone could have snuck into an airport and buried a bomb underneath the runway, then cleaned up the digging operation so as to not be noticed, but horses, not zebras.