First flight of the first prototype (EDM-1) for the CH-53K Type series
Tuesday, October 27, 2015 - Sikorsky Flight Development Center, West Palm Beach, United States of America
The first flight of the next generation variant of the CH-53 series of aircraft.
A description of the design and development history for the CH-53K is provided in the Wikipedia entry.
Source: Testing Kings, VERTIFLITE January/February 2016, Page 18