The only WWII battle in North America

In spite of my long-standing interest in the Second World War, I had no idea until this week that there was a full-scale battle on North American soil. The location was the island of Attu at the western-most reaches of the Aleutian chain.
The fighting was fierce and the death toll ran into thousands. You can read about the battle here.
What drew my attention to this little-known aspect of World War Two was a tiny item in a newspaper explaining that US and Japanese officials have just found four mass graves which they believe hold the remains of around 500 soldiers.