[Suhiir]

Well this is what I've found.
Since the first deliveries were apparently sometime in 1971 I'll stick to the 01/1972 operational deployment date since I can't find any definitive information.

"211 UH-1N ( Bell 212 ) were ordered for USMC service in late 1960s. Six ( plus 2 conversions ) were for presidential use (Marine One) as VH-1N and are listed separately. Many were later converted to HH-1N and turned over to US Navy as land based rescue/utility machines.
Deliveries of the twin huey (HH/UH-1N) to US Navy/USMC began in 1971. The last, and newest, UH-1N Iroquois was delivered in January 1979."

"Originating from a 1955 U.S. Army contract for a medical evacuation helicopter, the first Navy/Marine Corps Iroquois variant, the UH-1E, was first procured in 1964. Deliveries of the current version, the HH/UH-1N, began in 1971."