A prototype locomotive, initially classified EF90 and numbered EF90 1, was built by Kawasaki Sharyo in 1966.
It had a total power output of 3.9 MW (5,230 hp), making it the world's most powerful narrow-gauge locomotive at the time.

EF66 901 was retired from service in 1996, and has been stored at Hiroshima Depot since February of 2001, but it was taken apart in March.
A prototype locomotive, initially classified EF90 and numbered EF90 1, was built by Kawasaki Sharyo in 1966. It had a total power output of 3.9 MW (5,230 hp), making it the world's most powerful narrow-gauge locomotive at the time.
EF66 901 was retired from service in 1996, and has been stored at Hiroshima Depot since February of 2001, but it was taken apart in March.
JNR Class EF66