Among other Americanisms adopted by Okinawa during the post-War administration by US forces—such as an abiding love of A&W restaurants and SPAM—was the requirement to drive on the right, in contrast to the rest of Japan.
With the Vienna Convention on Road Traffic entering into force in 1977, and earlier 1949 Geneva Convention on Road Traffic, both requiring member states to have a uniform traffic direction throughout the country, post-occupation Japan was obliged to bring Okinawa in line with the rest of the country and international practice. Owing to assorted bureaucratic wrinkles, however, it was not until 1978 that Okinawa finally made the switch to left-hand drive.
Today, that switch is commemorated by the "730 Monument" in Ishigaki-jima, in the far south of Japan.