This is an exceptionally rare WWI Model No. 5 experimental helmet. From the outset of the war, the United States came to realize that its Brodie style helmet, modeled after the British design, insufficiently protected the wearer. To develop an improved helmet, the U.S. turned to Dr. Bashford Dean, curator of arms and armor at the Metropolitan Museum in New York City. In turn, Dean developed a series of 15 numbered prototype helmets. The Model No. 5, "was considered by Dean to be the most successful in terms of its defensive qualities, functionality, wearability, and practicality for mass production" (MET Museum). In 1918, the Model No. 5 underwent combat testing in France. To Dean's disappointment, the design was ultimately rejected by the U.S. due to its overall similarity to the silhouette of the German stahlhelm. This is one of just a few surviving examples produced by the Hale and Kilburn Company of Philadelphia, Pennsylvania. It is in very good condition. The helmet retains its original olive drab factory paint and textured finish. The interior features its original three-pad leather liner system and khaki chinstrap. The helmet's front pad has unfortunately become detached, revealing handwriting of likely an inspector. The khaki chinstrap is similar to those used on the M1917A1 helmet, with a cast-brass buckle and box stitching. If you've ever wanted an experimental helmet, you would be hard-pressed to find a more desirable example.