Premise: "Puritan" (ACM-16/MMA-16) was built for the United States Army as U.S. Army Mine Planter (USAMP) "Col. Alfred A. Maybach" MP-13. The ship was transferred to the United States Navy and classified as an auxiliary minelayer. "Puritan" was never commissioned and thus never bore the "United States Ship" (USS) prefix showing status as a commissioned ship of the U.S. Navy.
Hypothesis: Puritan was code named ACM-15