[Eric in the Ozarks]

The US Army rounded up hundreds, if not thousands of swords during the Occupation of Japan. When my dad got there in 1949 he was able to buy a matched pair (long sword and short sword with a throwing knife in the scabbard) from a private owner.
Many of these swords were taken out to sea and dumped.

[Age of Reason]

A lot of the ones the GI's brought back had their value greatly destroyed from being sharpened on grinding wheels.

[Lonesome in Massachussets]

History channel did a show on swords. They claimed that almost all the Samurai swords were sent to the U.S. after the War because the Japanese officers wouldn't retain them after they had been disgraced by defeat, so they became War trophies for lucky U.S. veterans.