It was done under...wait for it......The Clinton Administration... in 1994
You can construct some, but not all, of the components of U1, U2, ... U6 back to 1948 by using the www.bls.gov website. There were major changes in concepts and definition in 1994. However, I know that in the mid-1970s, the Monthly Labor Review published an article on these alternative unemployment rates.
The abstract of this article claims that the U1-U6 concepts were introduced in May 1976.
http://digitalcommons.ilr.cornell.edu/cgi/viewcontent.cgi?article=2353&context=key_workplace