Did basic (at 32 years old) in 2002. Our masks were the green C4 masks (They still are...Other than CANSOF)
I believe the ones that will be available for sale here are the C3 which were manufactured from 1960 to 1986 i believe. Being relplaced in the 1990s with the C4. I do not have a C4 hard to find, however the C3 i had was the most comfortable mask other than the Avon S10 and FM12.