Dating back from 1925, the Italian Army had engaged in experiments to find a new model of combat helmet that could replace the aging and not completely satisfactory Adrian helmet adopted in 1915; coupled to this was that the Adrian was originally a French design, and it was probably felt (under the fascist regime) that an Italian-designed model was more appropriate.

In 1932 after lengthy trials (with prototypes from many Italian and foreign firms) it was decided to adopt one of them as the M31 helmet. However this model (recognizable by the small crest on its top) was not completely satisfactory, because its cupolar blowhole design was not seen as being efficient, and was rather perceived as a structural weakness. By replacing it with three ventilation holes (two on the sides and one on the rear), the Model 33 was born, and was adopted with a circular? on November 29, 1934.^[2]

The M33 helmet saw its trial by fire in the Second Italo-Ethiopian War in October 1935. Shortly after the end of the second Italo-Ethiopian War. After the Spanish coup of July 1936, The Spanish Civil War started, Mussolini started supplying Francoist Spain under Generalissimo Francisco Franco, as part of the military aid to the nationalists, Italy provided the Nationalists with 660 planes, 150 tanks, 800 artillery pieces, 10,000 machine guns, and 240,000 rifles. (Italian military intervention in Spain) as well, Italy sent the Corpo Truppe Volontarie which was approximately 78,000 troops. When the troops withdrew at the end of the Spanish civil war on April 1, 1939, they left approximately 50,000-60,000 M33 helmets which saw use with the Spanish Army until the late 1970s, when they were surplused off after the end of the Francoist regime.

On June 10, 1940, Italy joined the Second World War, in September 1940. The Italian forces invaded Egypt from Libya, starting the North African campaign. Italian troops were mostly issued the Mod. 35 tropical helmet, Although the M33 still saw widespread use in North Africa. The M33 Helmet saw widespread use in North Africa and through the rest of the war. Some second line troops were also issued the Adrian helmet and a light weight version of the M33, (which are distinguishable by the absence of ventilation holes in the rivets).

When the Italian Civil War started in 1943, the M33 was obviously still the main helmet of both the Kingdom of the South and the Italian Social Republic. In 1944–1945, the British attempted to replace the M33 with the Brodie helmet; however only two divisions had switched by the time the war ended. Meanwhile, the US Army transferred some as well, but not enough to completely re-equip any large units. After some thought it was decided to retain the M33 and the brodie helmets were gradually phased out.

After WWII ended in 1945. It went on to have a long postwar career with the new Italian army. The M33 remained the standard Italian army helmet through the end of the 1980s. During the Cold War, production was restarted. Postwar-manufactured examples are nearly identical but have a slightly different interior headband, a different serial number scheme, and have a canvas chinstrap replacing the leather one of the 1930s and 1940s.

While not possessing the same degree of protection offered by the German Stahlhelm, the M33 was seen as a successful design, since it offered three times the resistance of the Adrian, was light at 1.2 kg, and was relatively comfortable.

The main users of the M33 helmet were:

•   Kingdom of Italy The M33 helmet (more formally, Elmetto Mod.33) was the standard helmet of the Italian army during WWII. It was designed in the early 1930s to replace WWI-era helmets. Made of 1.1mm heat-treated steel, the M33 was said to offer triple the protection of the French army's then-current Adrian helmet (Italy expected France to be its enemy in any future war). All in all, the M33 was effective, comfortable, and economical for Italy to manufacture during WWII. It was a quality helmet.
•   Albania Albania's use of the M33 is most interesting, as the helmet had two separate “tours of duty” in the country. When Albania was an Italian vassal between 1939 and 1943, its small puppet army was partially equipped with M33s. These continued in use when the communists took over in 1945, at the same time Soviet-made helmets began to replace them. Some M33s were still in use at the start of the 1950s, and the helmet was officially relegated to reserve warehouses at the end of 1952. Later during the Cold War, Chinese-made helmets replaced the WWII-era Soviet ones, which in turn displaced the M33s from warehouses for scrapping.
•   Argentina The Argentine army imported a small number of M33s during the late 1930s. They were not as popular as stahlhelms in Argentina, and only served a short while after WWII.
•   Francoist Spain Mussolini provided a quantity of M33s to Franco's civil war troops, with deliveries starting in 1938. While the M33 was never the “main” Spanish helmet type, a significant number were imported and served on long after WWII ended. As Spain remained neutral in the war, none were lost.

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    Socialist Federal Republic of Yugoslavia The JNA (Yugoslav Federal Army) used M33 helmets in the immediate post-WWII period, along with British, German, and Soviet helmets. These M33s were obtained from a number of sources. Some were captured during the war by partisans fighting Italian troops in what is today Kosovo and Macedonia, others were left behind when the Italians evacuated Dalmatia and Trieste at the end of the war. The Yugoslavs phased the M33 out in the early 1950s.
•   Peru The Peruvian army imported M33s in the late 1930s, replacing M34 French 'Adrian' helmets previously used. Its M33 supply was then bolstered by examples captured from Ecuador in July 1941. Peru continued to use the M33 until 1956.
•   Ecuador The army of Ecuador made a large buy of Italian helmets in 1938. Some were old surplus M15s (which the M33 replaced in Italian service) but more were new-production M33s. Ecuador fought a brief, one-month war against Peru in July 1941 (known as the Ecuadorian–Peruvian War) which resulted in an Ecuadorian defeat. Ecuador's forces were very poorly organized and many went into battle not having received their M33s, however, invading Peruvian troops captured a stockpile of them in an armory. Because of the loss, and the now-possibility of friendly fire mistakes in any future war against Peru, the Ecuadorian army phased out the M33 in the early 1940s and replaced it with American-made M1 pot helmets obtained as WWII military aid.
•   Republic of Bosnia and Herzegovina A handful of WWII-vintage M33s were found in use by the Bosniak Muslim forces during the 1990s conflict there. These were almost certainly ex-Yugoslav. and due to their small number, they may have been museum loots.
•   People's Republic of Bulgaria Designed in 1951, the Bulgarian M51 helmet was heavily influenced by Italian helmets. This style of helmet was used up until the 1990s with small variations in the shell, rivets, liners and chinstrap. The last variation of the helmet and is believed to have been introduced in 1972.

• Filippo Cappellano and Livio Pierallini, L'elmetto mod. 33, in Storia Militare n. 230 (November 2012)
• M33 Helmet Post War Use.

• The M31 and M33 helmet on the Italian Army website [Italian]