Albert)Although both of the buttons pictured below were made by the same manufacturer, D.
The difference is that the more common one during the Civil War, the NA112, had the upper fluke of the anchor behind the left wing, whereas the NA113 had the upper fluke of the anchor in front of the left wing.
These types were used right up through WWII, although the NA112 type became much less common after the Civil War.(source: , by Alphaeus H.
Many were American manufacturers; there were also several British and a few French manufacturers as well.
I am using many references to Albert’s button book, probably the best resource for US military uniform buttons.
His book, the first book listed below, is a must for US military button collectors, as well as various other references on buttons and backmarks.