The stamped, sheet steel construction helmet retains a good portion of its factory applied field-gray paint. All three liner retaining rivets are all intact. The interior of the helmet has a M31, tan, leather liner with all eight of its original fingers and size adjustment string. The interior, reverse, neck guard apron is serial number stamped, "2324" and has the stamped manufacturer’s code and size that appears to be, "ET66", indicating manufacture by Eisen-und Hüttenwerke, AG Thale/Harz, size 66.Excellent. The first "modern" steel helmets were introduced by the French army in early 1915 and were shortly followed by the British army later that year. With plans on the drawing board, experimental helmets in the field, ("Gaede" helmet), and some captured French and British helmets the German army began tests for their own steel helmet at the Kummersdorf Proving Grounds in November, and in the field in December 1915. An acceptable pattern was developed and approved and production began at Eisen-und Hüttenwerke, AG Thale/Harz, in the spring of 1916. These first modern M16 helmets evolved into the M18 helmets by the end of WWI. The M16 and M18 helmets remained in usage through-out the Weimar Reichswehr era and on into the early years of the Third Reich until the development of the smaller, lighter M35 style helmet in June 1935. In an effort to reduced construction time and labor costs minor modifications were introduced in March 1940 resulting in the M40 helmet. Further construction modifications were undertaken in August 1942 resulting in the M42 helmet.