The military base is located in Iwakuni, Japan and is one of the many American military bases scattered around the islands of Japan. Incidentally this is the second American base that I have visited in Japan, the first being the Yokosuka Navy base near Tokyo way back in 2005.
Iwanuki is located roughly 1 hour by train from Hiroshima city and 1 hour and 30 minutes from Higashi-Hiroshima (where I live now).
The event was quite popular and all the trains headed to Iwanuki were jam-packed.