The Aerospatiale SA366G1 Dauphin was selected by the United States Coast Guard in 1979 as its new short range recovery (SRR) air-sea rescue helicopter, replacing the Sikorsky HH-52A Sea Guard. In order to comply with american regulations relating to local content, engineering changes were required: most notably the french original Turbomeca Arriel engines were replaced with Lycoming LTS101 powerplants. The Dolphin normally carries a crew of four: pilot, copilot, flight mechanic and rescue swimmer.
1984 : HH-65A Dolphin
2001 : HH-65B Dolphin : first avionics upgrade
2006 : HH-65C Dolphin : re-engined and with new nose
2007 : The HH-65 is re-designated MH-65
2007 : MH-65C Dolphin. Replaced the MH-68A Stingray
2011 : MH-65D Dolphin. 97 aircraft with new avionics upgrade
2013 : MH-65E Dolphin. Glass cockpit similar to MH-60T Jayhawk
Serials: Bought new were 99 HH-65A plus 7 HH-65C
4101-4104 - test aircrafts
4105-4118 - original numbers ( changed later to 65nn )
4119-4123 - cancelled ?
6501-6598 - current ( ex 41nn included )
66nn - airframes received post 2000
Notice in the above video the little fan on the top of the main rotor. It is called the OADS (Omni-directional Air Data System), It spins around and measures differences in air pressure to indicate relative winds. The system was set to be removed in the MH-65D variant as it was extremely maintenance intensive and not very accurate.