Japan actually did bomb the mainland US during WW2 and it was, by definition, an unguided terror bombing. By 1943, the Japanese military realized that they had a unique advantage over the US (and Canada) called the prevailing wind. Using a hydrogen balloon made of laminated paper and a well thought out timing and flight plan, Japan could unleash thousands of incendiary and even biological bombs on the western US.
Implemented in 1944, it is estimated that only about 20% of these devices made it to the US and Canada but at least one made it all the way to Michigan. In May of 1945, one of these caused the only mainland US casualties of WW2 when a church camp group in southern Oregon set one off. The US Government had known and kept secret this Japanese campaign because it feared that news would encourage a much larger campaign by the enemy. Since these weapons were near impossible to spot en-route, were easy & inexpensive and potentially very deadly if used for rabid bats or worse, this was a high government secret.
Maybe, even today's liberal media would have kept it a secret, MAYBE!
There was more than that.
Japanese submarines operated in California and Oregon's coastal waters. A refinery in Southern California was shelled with submarine deck guns, ships were sunk (such as the Emidio, off of Crescent City, CA, and a submarine launched aircraft dropped incendiary bombs in the Oregon forests east of Brookings, OR.
http://www.eugeneleeslover.com/Japanese_bomb_Oregon.html
Long after the war's end, the Japanese pilot was invited back and given the celebrity treatment. He helped dedicate a memorial and made a gift of his sword.