Some M1 helmets and their derivatives remain in service with several national militaries in the 21st century, although most have been relegated to being part of certain ceremonial uniforms, such as those of honor guards.

[3] At that point, the shortcomings of the M1917, which lacked balance and protection of the head from lateral fire, resulted in a project to produce a better helmet which would also have a distinctively American appearance.

[4] This was an improved version of the Helmet Model Number 5, developed in 1917 and 1918 by Bashford Dean, the curator of arms and armor at the Metropolitan Museum of Art,[5] which had been rejected during the war because of its supposed resemblance to the German Stahlhelm.

Further ballistic tests at the Aberdeen Proving Ground resulted in the decision to retain the M1917 in 1934,[4] which was then given a redesigned leather cradle and designated the M1917A1[7] or "Kelly" helmet.

The Infantry Board resurrected the quest to find a better type of helmet, since the ongoing conflict had shown that the M1917, designed to protect men standing in trenches from falling shell splinters and shrapnel, would be inadequate on the modern battlefield.

The board reported: Research indicates that the ideal shaped helmet is one with a dome-shaped top and generally following the contour of the head, allowing sufficient uniform headspace for indentations, extending down in the front to cover the forehead without impairing necessary vision, extending down on the sides as far as possible without interfering with the use of the rifle or other weapons, extending down the back of the head as far as possible without permitting the back of the neck to push the helmet forward on the head when the wearer assumes the prone position, to have the frontal plate visor and to have the sides and rear slightly flanged outward to cause rain to clear the collar opening.

[9]Accordingly, the board, under the direction of Brigadier General Courtney Hodges,[10] took the M1917 shell as the basis of the new prototype, trimmed off the brim, and added a visor and skirt-like extensions to protect the back and sides of the wearer's head.

In tests, they were found to be able to resist a .45 ACP pistol bullet fired at point-blank range, exceeding the initial specification.

Postwar analyses of wartime casualty figures by the U.S. Army Operations Research Office found that 54 percent of hits to the M1 helmet failed to penetrate, and estimated that 70,000 men had been saved from death or injury by wearing it.

The M1 is a combination of two "one-size-fits-all" helmets—an outer metal shell, sometimes called the "steel pot", and a hard hat–type liner nestled inside it featuring an adjustable suspension system.

After being poured into fifteen-ton ingots (also called "heats"), the steel was divided into 216-inch by 36-inch by 4-inch blocks, known as "lifts," which were then cut into three equal 72-inch pieces to make them easier to handle.

The helmet discs were oiled and banded into lots of 400 for delivery by rail to McCord or Schlueter for pressing and final assembly.

1950s and later production chinstraps are made of olive drab webbing attached to the loops with removable metal clips.

This practice arose for two reasons: First, because hand-to-hand combat was anticipated, and an enemy could be expected to attack from behind, reach over the helmet, grab its visor, and pull.

If the chinstrap were worn, the head would be snapped back, causing the victim to lose balance, and leave the throat and stomach exposed to a knife thrust.

In place of the chinstrap, the nape strap inside the liner was counted on to provide sufficient contact to keep the helmet from easily falling off the wearer's head.

Three triangular bands of rayon meet at the top of the helmet, where they were adjusted by a shoestring to fit the height and shape of the wearer's head.

Early liners were made from a mix of compressed paper fibers impregnated with phenolic resin, with olive drab cotton twill fabric stretched over the outside.

Hawley, Hood, and St. Clair's contracts were cancelled by early 1944, when a "high pressure" process which produced better-quality liners became commercially viable.

The U.S. Army often used nets to reduce the helmets' shine when wet and to allow burlap scrim or vegetation to be added for camouflage purposes.

A consignment of 100,000 olive drab covers was dispatched to the theater, but the ship carrying them, SS Jacob Luckenbach,[26] sank in a collision en route and they were all lost.

During the Battle of the Bulge and the Korean War, soldiers made white helmet covers as camouflage in snowy areas.