This is a Significant Operational milestone.
This the day that is recognised as dao on which United States Coast Guard (USCG) started to operate rotary wing aircraft. This date was marked by the delivery of the first Sikorsky HNS-1 procured by the US Navy (the Coast Guard had been assigned the task of developing the helicopter for naval operations). The aircraft was accepted on behalf of the USCG by Commander Frank Erikson.
Source: "Lifesaving, Law-Enforcing Vertical Lift", Frank Colucci, VERTIFLITE May/June 2019, Volume 65, Number 3, Page 77