This is a Notable Technology milestone.
This was a program sponsored by the Office of Naval Research, using a Kaman HTK-1 as the test vehicle (designated HTK-1K)
A video of the aircraft in flight can be seen by selecting the link below,
Kaman HTK-1K - the first unmanned helicopter, by sobchakvideos, YouTube, accessed Mar 29 2017
Source: "The Kaman Aircraft Corporation", Charles Kirchner, Journal of the American Helicopter Society, Volume 1, Number 1, January 1956, Page 54
Note: The exact day for this milestone is unknown