King Stallion Summer: CH-53K to enter operational test in July By Dan Parsons | April 23, 2021 Estimated reading time 13 minutes, 50 seconds. A fleet of four CH-53K King Stallions this summer will begin the final leg of testing for the U.S. Marine Corps’ new heavy-lift helicopter ahead of its entry to service in 2023, but work remains to ensure that milestone doesn’t slip to the following year. The Marine Corps is in the final throes of wringing out its several engineering and manufacturing developmental 53K models ahead of initial operational test and evaluation (IOT&E) with aircraft representative of what Marines will fly. Marines now have their hands on three production aircraft and are training to fly and maintain them at Marine Corps Air Station New River in North Carolina.