"Boeing delivered more than six hundred H-46 Sea Knights to the US Marine Corps and Navy from 1964 through 1971, and most of them are still flying. It will be replaced in Marine Corps service by the V-22 Osprey ‘tilt rotor’ but according to the latest reports the H-46 will be in use until 2012, a service life of forty-eight years. The Marines joke "If it was good enough for my Father (by now occasionally Grandfather), it’s good enough for me."
The Marines used the 'Phrog' in Vietnam and still today, to transport personnel and cargo, from ship to shore and point to point on land, landing troops for assault and resupplying them afterwards. It has been put to every possible use; VIP transport, SAR, and in Vietnam, medical evacuation (medevac), anything and everything the Marines needed it for."
I guess this will replaced sooner, than later!