There were eight versions of this helmet developed during WWI. All are very similar in appearance and vary only in regard to weight and some features, such as the sliding visor on No. 8, which was designed for machine gunners. No. 5 helmet, which weighed 2 pounds, 6.5 ounces was considered the most successful of the series in that it combined all the best features of the other helmets. The Swiss Army adopted the No. 5 model as its standard helmet. The photos and information are from America's Munitions, 1917-1918, Report of Benedict Crowell, Assistant Secretary of War for Munitions, Washington: GPO, 1919, pp. 223-26 Dwight
Photos showing full body armor developed by Ordnance Dept. in WWI
Upper left is helmet No. 2 and upper right is helmet no. 8 with the visor up.