The R-27 Zyb missile carried by the Project 667s of the late 1960s had a range of just , so the earlier subs were forced to patrol close to the North American coast, whereas the Deltas could launch the >-range R-29s from the relative safety of the Arctic Ocean. In turn the Deltas were superseded by the larger Typhoon class submarines. The early Deltas remained in service until 1990s with treaties such as START I. High running costs and the retirement of the Typhoons′ R-39 missiles meant that some Delta III's were reactivated in the 2000s (decade) to replace the Typhoons.