These blankets have been made by eight generations of the same family at the USA's longest continuously operating woolen mill ( Woolrich ), founded in 1830. This blanket was issued to all mounted troops, Cavalry, Artillery, Officers or anyone who rode a horse.
As per the 1863 Revised U.S. Army Regulations, page 479, paragraph 1647: "SADDLE BLANKET â€“ To be of pure wool, close woven, of stout yarns of an indigo-blue color, with an orange border 3 inches wide, 3 inches from the edge. The letters U.S., six inches high, of orange color, in the center of the blanket. Dimensions: 75 inches long, 67 inches wide; weight, 3.19 pounds; variation allowed in weight, 0.19 pounds." (Note: this is the same saddle blanket as described in the 1861 regulations)
Unidentified Union Trooper with M1859 McClellen Saddle and Horse Blanket.