At some point after the war, the peacoat underwent a major change. The number of buttons showing on the front of the coat changed from eight to six. This change lengthened and widened the lapel, which allowed it to lie flat against the body of the coat. It made for a neater presentation while only allowing a slightly larger opening at the top of the chest. The dense smooth wool outer shell remained unchanged, with a few exceptions. In the 70s there was at least one contract for the Melton wool, which became the standard shell from 1980 to present. The color remained the deep midnight blue in these Melton contracts. All of the pre-1980 peacoats I have seen that have Melton wool shells are labeled as such.
Post WWII coat
1947 and earlier tag
While the coats themselves remained unchanged for almost 35 years (1946–1979), there were numerous tags used during this period. It is this practice that makes dating these pieces of history accurate within a several year period. As the peacoats remained relatively unchanged until about 1980, the remainder of the discussion will focus on the uniqueness of the tags to establish a date for the coats.
My 1949 coat has the nicest finish of any of my coats. It has the standard 6 button (showing) front with double stitching on the sleeves, about 3" up from the end of the cuff, and a single row of stitching right at the cuff. It has the “Naval Clothing Depot” tag. I believe this tag was used up until about 1950 or 1951.