For some of the early Polaris submarines, the Polaris A-3 was the end of their upgrades, but a large number of them (about 31) were further rearmed with the more-advanced and longer-ranged two-stage Poseidon C-3 missile.
The early Polaris submarines were initially upgraded with the Polaris A-3, but a substantial number of them were later equipped with the more advanced and longer-range Poseidon C-3 missile.