Which of the following is NOT one of the original CPO rates?

The original Chief Petty Officer (CPO) rates in the U.S. Navy were established as part of a transformation in the ratings system to create a more effective leadership class within the ranks. The rates that were originally designated as CPOs included Boatswain's Mate (BM), Yeoman (YN), and Hospital Corpsman (HM), among others. The Engineering (ENG) rate, while certainly a crucial role within the Navy, did not exist as a distinct CPO rate in the original establishment.

The distinction here is based on historical significance and organizational structure; the CPO ranks were intentionally shaped to reflect the vital operational and administrative roles necessary for the Navy's functionality during the time of their inception. Hence, identifying ENG as not one of the original CPO rates underscores the clarification of roles as they were divided and evolved in the Navy's history.