So? The Japanese had been at war for about seven years by 1943, and they would be bringing tanks, mortar and artillery with them.Citizens soldiers have a long history in the USA, the british did not do very well. Not many country has the guns the USA does or a people that have been handling guns alll their lives. I think the Japnese would have been in for a nasty susprise.
And unlike the British during the war of independence, they wouldn't have any qualms about burning entire cities to the ground, leaving any guerrillas without safe havens.