The T-100 was originally conceived with three turrets and was eventually built with two. It was in competition with a similar design - the SMK - but neither were adopted and instead a single turret version of the SMK was ordered as the KV-1.
Originally conceived with three turrets, the T-100 was later constructed with only two. It competed with another design, the SMK, but neither won; instead, a single-turreted version of the SMK was ordered to become the KV-1.