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Bicorne -

The two-cornered hat known as a bicorne was widely adopted in the late 1800s by American and European army and naval officers. French emperor Napoleon Bonaparte famously wore his side-to-side, and it's pictured here.

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Bearskin -

The tall fur cap known as a bearskin is synonymous with British foot guard regiments. Initially worn only by grenadiers in the 17th and 18th centuries, it was later adopted by several other military units, including foreign regiments, in the 19th century. Today it's worn only as part of ceremonial uniforms, for example by the British Coldstream Guards.

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Green beret -

The United States Army Special Forces are colloquially known as the "Green Berets" due to their distinctive service headgear. The term is apparently credited to John F. Kennedy, who in 1962 visited Fort Bragg/Liberty and observed a Special Forces training demonstration. The participants all were wearing forest green French berets.

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Shako -

A tall, cylindrical military cap, the shako was used as an item of military headgear during the 19th and early 20th centuries. First worn by Hungarian hussars, the shako was eventually worn by the majority of regiments in the armies of Europe and the Americas.

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Terai hat -

Associated with the Gurkhas for decades, the Terai hat is named after the Terai region of Nepal. The Gurkhas are elite soldiers native to the Indian subcontinent, chiefly residing within Nepal and some parts of North India.

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Peaked cap -

The peaked cap is arguably the most recognized of military headgear, worn by the armed forces of numerous nations. The cap actually has a civilian heritage, popular as it was in late 18th century when it was worn mostly by working-class men across northern Europe.

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Dragoon helmet -

This 19th-century leather and gilded helmet was worn by the Piedmont dragoons, members of the Savoy-Piedmont-Sardinian armies. The term "dragoon" comes from the nickname for their weapon, the carbine or short musket, called "the dragon," which referred to the fire that emitted out of the gun when fired.

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Farion cap -

The farion cap is worn by members of the Greek Presidential Guard, or Evzones. The fermeli, or tassel, is hand-sewn entirely from wool.

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Sailor cap -

There are numerous versions of the sailor cap, a round, flat visorless hat worn by sailors in many of the world's navies. Illustrated here is the "dixie cup" worn by members of the United States Navy.

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Pith helmet -

The origin of the pith helmet is the traditional Filipino headgear known as the salakot. The Spanish military adapted the design for use in the 18th century. Pith helmets were widely worn during the First World War by various armies operating in the tropics and hot, arid environments. The pith today is mostly worn by guards of honor and military marching bands.

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Hardee hat -

The Hardee hat was the regulation dress hat for enlisted men in the Union Army during the American Civil War. Named after William J. Hardee, a career officer in the US Army, the hat made its debut in 1855.

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Glengarry bonnet -

First worn in 1794 by members of the Highland Fencible Corps, the Glengarry bonnet is a traditional Scottish cap made of wool. It's normally worn as part of Scottish military or civilian Highland dress.

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Kepi -

The kepi was formerly the most common headgear in the French Army. A cap with a flat circular top and a peak, or visor, the kepi was famously worn by General Charles de Gaulle of the French Free Forces in this 1942 portrait.

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US Civil War kepi -

In North America, a version of the kepi was worn by both sides during the American Civil War.

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Tricorne hat -

The tricorne was not only worn as part of military and naval uniforms, but also by the aristocracy, such was its popularity in the 18th and 19th centuries. Tricorne hats are regularly worn by Chelsea Pensioners, former members of the British Army who reside at Royal Hospital Chelsea retirement home in London.

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Busby -

Busby is the English name for a shako. This example was worn by a member of the German hussar regiment, around 1910.

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Maroon beret -

Synonymous with the parachute regiment, the airborne and elite infantry regiment of the British Army, the maroon beret has in fact been an international symbol of airborne forces since the Second World War.

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Pickelhaube -

Worn in the 19th and 20th centuries by Prussian and German soldiers of all ranks, the pickelhaube is a spiked leather or metal helmet and is still adopted by some militaries today as ceremonial headdress.

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Redcap -

Members of Great Britain's Royal Military Police are often known as "Redcaps" because of the scarlet covers on their peaked caps and scarlet colored berets.

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Lobster-tailed pot helmet -

Derived from an Ottoman Turkish helmet type, the lobster-tailed pot helmet became popular in 1600s Europe and was worn by officers and cavalrymen. In England, Oliver Cromwell's civil war-era "Roundheads" wore helmets similar in design.

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Caubeen -

In the 16th century, the caubeen, or Irish beret, was worn as an item of civilian headgear. By the 18th century, it had been adopted as the head dress of Irish regiments of Commonwealth armies. The name caubeen literally means "old hat."

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Cuirassier helmet -

Cuirassiers were cavalry equipped with a cuirass, sword, and pistols. They first appeared in Europe in the late 16th century. Depending on the regiment, cuirassier full dress uniform included the wearing of a helmet with chromium-plated decorated cap, surmounted by a gilded metal crest with tail.

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Albert helmet -

The Albert helmet was developed by, and named for, Prince Albert, the husband of Queen Victoria, in 1842. It's worn as a type of full dress headgear used by several British and Canadian cavalry regiments, including Blues and Royals and the Life Guards of the British Household Cavalry.

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Cavalry Stetson -

Typically worn by cavalrymen of the United States Army in the late 1860s, the Cavalry Stetson was named after its creator John B. Stetson (1830–1906). The yellow cord denotes non-commissioned officer status.

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Cappello Alpino -

The unique and iconic headdress used by the Alpini features a black raven feather and the fregio, a coat of arms indicating the wearer's regiment. The Alpini are the Italian Army's elite mountain combat division.

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Military turban -

The turban has been a tradition for Sikh soldiers serving in the British armed forces for many years, and is now part of their uniform. Sikhs serving in the military police in India also wear specially adapted turbans.

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Turban helmet -

Turban helmets originated in the 15th century, perhaps in Iran but more likely in Ottoman Turkey. As the name suggests, they were designed to imitate the folds of a turban and were worn by warriors.

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Fez -

A characteristic symbol of the Ottoman Empire, the fez was used as a modern headdress for the army of Mahmud II in 1827. In 1925, the fez was outlawed in Turkey as part of Atatürk's reforms. Since then, it has not been a part of Turkish men's clothing either in a civilian or military capacity.

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Forage cap -

A practical though somewhat unattractive item of military headgear, the forage cap, also known as an undress cap, was worn as fatigue or working headwear by many soldiers of different nations throughout the 19th century and into the 20th century. The name comes from the habit of cavalrymen foraging for food for their horses.

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Rogatywka -

Rogatywka is the Polish generic name for a peaked, four-pointed cap used by various Polish military formations throughout the ages. The example pictured here features a military eagle, the emblem of Polish armed forces, and three stars, the rank insignia of a pułkownik (colonel).

Sources: (Trimtag) 

See also: What police uniforms look like around the world

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