Editing M1 helmet (section)

== Design ==
[[file:M60 machine gun DA-ST-84-04992.jpg|thumb|A U.S. Army machine-gunner wearing an M1 helmet with a [[military camouflage|camouflage]] cover and additional natural camouflage added on the slots in the helmet's cover]]

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. Helmet covers and netting would be applied by covering the steel shell with the extra material tucked inside the shell and secured by inserting the liner.

The outer shell should not be worn by itself. The liner can be worn by itself, providing protection similar to a hard hat, and was often worn in such fashion by military policemen, Assistant Drill Instructors (known as AIs), and rifle/machine gun/pistol range staff, although they were supposed to wear steel at the range.{{Citation needed|date=November 2010}} The liner is sometimes worn in U.S. military ceremonies and parades, painted white or chromed.{{Citation needed|date=November 2010}} The depth of the helmet is {{convert|7|in}}, the width is {{convert|9.5|in}}, and length is {{convert|11|in}}, the steel shell thickness is {{convert|0.044|in|mm|abbr=on}},{{clarify|Confusing. Below it says the metal disks for stamping were 0.04 in thick. Other dimensions here or shell dimensions, and “thickness” should reflect that.|date=June 2020}} The weight of a World War II-era M1 is approximately {{convert|3|lb}}, including the liner and chinstrap.

=== Shell ===
[[file:M60 101st Airborne Division Exercise 1972.jpg|thumb|left|[[101st Airborne Division]] soldiers wearing M1 helmets during a [[training exercise]] in 1972]]

The non-magnetic [[Mangalloy|Hadfield manganese steel]] for M1 helmet shells was smelted at the [[Carnegie Steel Company]] or the Sharon Steel Company of [[Pennsylvania]]. 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 cut lifts were sent to the [[U.S. Steel|Gary Works]] in [[Gary, Indiana]] for further processing, after which they were each reduced into 250 68-inch by 36-inch by 0.044-inch sheets, which were cut into 16.5-inch circles. The helmet discs were oiled and banded into lots of 400 for delivery by rail to McCord or Schlueter for pressing and final assembly.<ref>{{cite journal|last1=Giles|first1=Marc|date=2018|title=M1 Helmet Lot Numbers|journal=Military Collector and Historian|volume=70|issue=3|pages=258}}</ref>

Each "heat" of steel was assigned a unique number by the smelter, as was each of its "lifts". When each new heat was unloaded at McCord or Schlueter, it was assigned a sequential number, and each lift within the heat was assigned a letter of the alphabet (for example, the third lift unloaded of the forty-ninth heat received by McCord would be 49C). This unique "lot and lift" number was stamped onto each helmet produced from the discs of a particular lift, and allowed for traceability in case the helmets exhibited defects. The "lot and lift" number is in reference to the time when the fabricator received the helmet discs, not when they were made into finished helmets. Lifts of heats were not loaded onto or unloaded from railcars in any particular order, and were often warehoused (also in no particular order) before being finished.<ref>{{cite journal|last1=Giles|first1=Marc|date=2018|title=M1 Helmet Lot Numbers|journal=Military Collector and Historian|volume=70|issue=3|pages=260}}</ref>

The helmet discs were [[Drawing (manufacturing)|drawn]] to a depth of seven inches to create the rough helmet shape, or "shell," and the edges were trimmed. The edge of the shell has a crimped metal rim running around it, which provides a smooth edge. This is usually known as the "rim". The rim has a seam where the ends of the strip meet. On the earliest shells the seam met at the front. This was moved to the back of the rim in November 1944<ref>{{Cite web|url=http://www.hardscrabblefarm.com/ww2/dating_m1.htm|title=Dating the M1 Steel Helmet|website=www.hardscrabblefarm.com|access-date=2019-05-05}}</ref> At this time, the rim also went from being made of stainless steel to manganese steel. On each side of the shell, there are stainless steel loops for the chinstrap. Early-war production shells had fixed rectangular loops, and mid-war to 1960s helmets feature movable rectangular loops; this feature was adopted in 1943 to address the problem that when earlier helmets were dropped, the fixed loops were more susceptible to breaking off. Early shells for paratrooper helmets feature fixed, D-shaped loops. The shells were then painted with flat Olive Drab shade 319 (1941–1966) or Munsell Y10 green paint (1966 onward), with the paint on the outside of the shell sprinkled with either finely ground cork (World War II era) or silica sand (postwar).

[[file:Albert Hoeben RMWO.jpg|thumb|upright|An M1 helmet with camouflage cover worn by a [[Netherlands Marine Corps]] corporal in 1945]]
World War II-production helmets feature sewn-on cotton web olive drab shade 3 chinstraps, replaced gradually throughout 1943 and 1944 with olive drab shade 7 chinstraps. 1950s and later production chinstraps are made of olive drab webbing attached to the loops with removable metal clips. Nylon chinstraps were introduced in the U.S. military in 1975. These straps featured a two-piece web chin cup and were fastened by a metal snap rather than buckle.<ref name="Brayley2008_p.123"/>

Many soldiers wore the [[webbing]] chinstraps unfastened or looped around the back of the helmet and clipped together. 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. Secondly, many men incorrectly believed that a nearby exploding bomb or artillery shell could cause the chinstrap to break their neck when the helmet was caught in its concussive force, although a replacement buckle, the T1 pressure-release buckle, was manufactured that allowed the chinstrap to release automatically should this occur. 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.<ref>{{cite news |last=Tagliavini |first=Michele |url=https://www.theguardian.com/notesandqueries/query/0,,-2696,00.html |work=[[The Guardian]] |location=London |access-date=8 March 2013|title=STAGE AND SCREEN In all those Hollywood war films, and in quite a few newsreels, the GIs wear helmets but never fasten the straps. Is this bravado, bad discipline or artistic licence?}}</ref>

The design of the bowl-like shell led to some novel uses: When separated from the liner, the shell could be used as an [[entrenching tool]], [[hammer]], [[washbasin]], [[bucket]], [[bowl]], or [[seat]]. The shell was also used as a [[cooking pot]], but the practice was discouraged as it would make the metal alloy brittle.<ref>{{cite web|last=Pike|first=John|title=M1 Steel Combat Helmet and Liner|url=http://www.globalsecurity.org/military/systems/ground/m1-steel-pot.htm|work=GlobalSecurity.org|access-date=8 March 2013}}</ref>

=== Liner ===
[[file:M1HelmetDiagram.gif|thumb|left|The interior of an M1 helmet liner]]

The liner is a hard hat-like support for the suspension, and is designed to fit snugly inside the steel shell.

The first liners were produced in June 1941 and designed by [[Hawley Products Company]].<ref name="Giard">{{cite book|last1=Giard|first1=Regis|title=Helmets of ETO: A Historical and Technical Guide|date=2008|publisher=Casemate Publishers|location=Havertown, PA|isbn=9782352500629|page=12}}</ref> The suspension was initially made from strips of silver rayon webbing stretched around and across the inside of the liner. A sweatband is clipped onto these, and is adjusted to fit around the head of the wearer. 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. A snap-on nape strap cushioned the liner against the back of the wearer's neck and stops it from falling off. As the rayon had a tendency to stretch and not recover its shape, the suspension material was later changed to olive drab number 3, and then olive drab number 7, herringbone twill cotton webbing.

World War II and Korean War-era liners have their own chinstrap made from brown [[leather]]. The liner chinstrap does not have loops like the shell; it was either riveted directly to the inside of the liner (early examples) or snapped onto studs. It can still swivel inside the liner. The chinstrap is usually seen looped over the brim of the shell, and helps to keep it in place when its own chinstraps are not in use.

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. They were discontinued in November 1942 because they degraded quickly in high heat and high humidity environments. They were replaced by evolving [[plastic]] liners,<ref name="Giard" /> using a process developed by the Inland Division of [[General Motors]]. These liners were made of strips of cotton cloth bathed in phenolic resin and draped in a star shape over a liner-shaped mold, where they were subjected to pressure to form a liner. The initial "low pressure" process was deemed unacceptable by the Army, but accepted out of need. These liners were made by St. Clair Manufacturing and [[Hood Rubber Company]]. 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. Companies which produced "high pressure" liners during World War II included [[Westinghouse Electric (1886)|Westinghouse Electric & Manufacturing Company]], [[Firestone Tire and Rubber Company]], CAPAC Manufacturing, Inland (whose molds were acquired by Firestone after their contract was cancelled), [[Mine Safety Appliances]] Company, [[Seaman Paper|Seaman Paper Company]], and International Molded Plastics, Inc.<ref name="Giard" />

Liners essentially identical in construction to "high pressure" World War II examples were produced between 1951 and 1954 during the [[Korean War]] by the Micarta Division of Westinghouse and CAPAC Manufacturing. In the 1960s, the M1 helmet liner was redesigned, eliminating the leather chinstrap, nape strap, and changing the suspension webbing to a pattern resembling an asterisk in a coarse cotton web material in lieu of the earlier cotton herringbone twill. In the early 1970s, suspension materials changed to a thicker, more flexible nylon with a rougher unbeveled rim. Later changes included a move to a yellow and green material for liner construction.

M1 helmet liners intended for use by paratroopers had a different construction. The short piece of webbing which held the nape strap at the back of the wearer's neck was extended around the sides of the liner, and terminated on each side in A-shaped yokes which hung down below the rim of the liner and had buckles for an adjustable chin cup made of molded leather. Two female snaps on the inside of the liner above the "A" yokes accepted male snaps on each of the steel shell's chinstraps, and helped to keep the liner inside the steel shell during abrupt or violent movements.