From the introduction of the Flues Model, both the Field Grade and the No. 1 Special used frames grade marked with an S as the frames for those two grades were the same.
The Field Grade was fitted with smokeless powder steel barrels and a half-pistol grip stock.
The No. 1 Special had a capped pistol grip stock and Cockerill Steel barrels.
The No. 1 was similar but fitted with Twist Steel barrels --
The No. 1 1/2 got a bit of zig-zag border engraving and was fitted with Damascus Steel barrels --
Then in mid-1915 Ithaca changed their engraving patterns to the bold McGraw styles, and the No. 1 1/2 got bold floral engraving --
Pretty quickly after that The Great War cut off the supply of composite iron and steel barrel tubes from Belgium. As Ithaca phased out Twist and Damascus barrels in every Ithaca catalog for 1916, 17 and 18 there were changes in these entry-level guns. The No. 1 Special was dropped, the No. 1 got steel barrels and zig-zag border engraving. June 1918 catalog --
Finally between the July and December 1919 catalogs they combined the surviving No. 1 and No. 1 1/2 as the New No. 1 --