Submarines have traditionally been the strongest component of the Northern Fleet. Several new classes of submarines are in production to replace older models including: Borei/Dolgorukiy-class SSBNs, Yasen-class SSGNs, Khabarovsk-class SSGNs and Lada-class conventionally-powered submarines. However, the existing nuclear-powered submarines of the Northern Fleet are also aging rapidly. It is currently unclear whether the new Yasen-class, and other potential follow-on models, can be produced in sufficient numbers, and on a timely basis, to replace aging older nuclear submarines on a one-for-one basis. In this regard, reports suggest that Russian third-generation nuclear submarines have not been modernized to a level to avoid block obsolescence before 2030.