A stopgap upgrade to the KV series was the short-lived KV-85 or Objekt 239. This was a KV-1S with the new turret from the Object 237 (IS-85) still in development, mounting the same 85 mm D-5T gun as the SU-85 and early versions of the T-34-85 (not yet in production at the time). The 85 mm proved capable of penetrating the Tiger I from 1000 m and the demand for it slowed production of the KV-85 tremendously, only 148 were built between August and October 1943. Soviet industry was therefore able to produce a heavy tank as well armed as the Tiger I before the end of 1943. Although the KV-85 was an excellent opponent to the Tigers and Panthers, it was a stopgap and thus was built in small numbers. The complete Object 237 was accepted into service as the IS-85 and was produced in the autumn and winter of 1943-44; they were sent to the front as of October 1943 and production of the IS-85/IS-1 was stopped by the spring of 1944 once the IS-122/IS-2 entered full-scale production.