General Information: The Model 1917A1 was a modified version of the World War One Model 1917. It was the helmet worn by all branches of the US Armed Services in the opening months of the Second World War before the M-1 became widely available.
The US Army issued a Field Service Modification Order in January of 1936 requiring the modification of all M-17 helmets. The modification involved replacing the liner with one that provided greater stability than the older style. In addition, the M-17A1s were equipped with new canvas chinstraps with a hook and receiver buckle of the type that had been used on experimental helmets produced around the end of WWI. The updated M-17A1 were frequently repainted shades of olive drab using paint textured with bits of cork to reduce reflectiveness. One external difference between the earlier and later versions of the helmet is that the M-17A1 had a prominent rivet at the top to attach the liner assembly.
Most of the M-17A1s were made from reissued M-17s, but in late 1940 the McCord Radiator and Manufacturing Company won a contract to produce nearly two million M-17A1 helmets. McCord began deliveries of the new helmets in February 1941 and completed production of approximately 900,000 by the time the US government cancelled orders for the M-17A1 in May of 1941. Subsequently, McCord switched to production of the M-1s.
The M-17A1s were, and still are, often referred to as the “Kelly” helmets. Documentation as to why this is so is nonexistent as far as I have been able to determine. With the help of collectors from the US Militaria Forum, we have a plausible explanation. “Kelly” is a now archaic term for a type of men’s hat. There are First World War period references to the M-17 as a “tin Kelly.” There are other references to the M-17 and the British version, the MKI, as “battle bowlers” or “tin derbies.” The British commonly referred to the MKI as a “tin hat.” Comparisons to civilian hats, therefore, were fairly common. It seems logical that “Kelly” was a shortened version of “tin Kelly.” It is a reference that would likely have been understood by people from the era.
Displayed Example: I got this perfect specimen years ago from my great helmet collecting buddy, Tom Buck. It is a classic, unaltered example of the type.
Collector Notes: The M-17A1 is not a difficult helmet to find and they tend to be priced at the lower end of the cost spectrum. They are iconic relics that recall the tragic opening conflicts for US forces in Pearl Harbor, Bataan, and Wake Island.
* Source: Life Archive. Complete original citation sought. http://www.90thidpg.us/Equipment/Reviews/PFLCo1917a1Liner/index.html.
 Armold, C. 1997. pp68-76
 Reynosa, M. 1997. pp12
 Why is it called a “Kelly” helmet? US Militaria Forum. June 9-12, 2022. https://www.usmilitariaforum.com/forums/index.php?/topic/372409-why-is-it-called-a-kelly-helmet/. Accessed June 15, 2022.