This double-visor modified APH-6A belonged to  Marine Attack Squadron (All Weathear) 225 „Vikings“ ,flying Grumman A-6A Intruder, DA NANG AIR BASE, 1969 

During 1965 the  Vikings were deployed at Chu Lai Air Base in South Vietnam while flying Douglas A-4C Skyhawk. At the end of the same year they returned to Cherry Point MCAS and transitionned to the Grumman A-6A Intruder, becoming  All Weather  capable.

In 1969 the squadron returned to Vietnam, this time at Danang Air base, flying night and day CAS missions. 

The Vikings returned from Vietnam in 1971.

Since this helmet is a modified APH-6A , it could have been used by VMA(AW)-225 before their 1969 Vietnam deployment, or early in the same deployment. From their 1969 Cruise Book, it seems that the squadron soon adopted green-painted flight helmets.