The name "caubeen" dates from late 18th century Irish, and literally means "old hat". It is derived from the Irish word cáibín, meaning "little cape", which itself is a diminutive form of cába, meaning "cape".
In the British and Canadian armies, the caubeen is officially known as the "Bonnet, Irish, Green".
In 1916, the British army regiment the Irish Guards established a pipe band. The pipers' uniform was a mix of standard service dress and bandsman dress, and also included a khaki bonnet, saffron-coloured kilts and green hose. The khaki bonnet was named "caubeen" by the Guards pipers, and was similar to an oversized beret. Some sources have stated the Caubeen's similarity to the Scottish tam o' shanter, but the two are different in appearance - the tam o' shanter retaining much more of a 'dinner-plate' effect on the wearer's head, while the Caubeen resembled an oversized beret. The two had different quartermaster codes, meaning that the Caubeen was not simply a tam o' shanter with the toorie cut off, but a purpose-made article in its own right. In World War II, a number of British army regiments adopted both khaki and rifle-green caubeens as their headdress, replacing the GS cap.
Each regiment was distinguished by the feather hackle in their caps: the Royal Inniskilling Fusiliers wore their traditional grey hackles, the Royal Irish Fusiliers wore their traditional green hackles, the Irish Guards and London Irish Rifles were granted blue hackles, and the Liverpool Irish wore a blue-and-red hackle. The Royal Ulster Rifles did not get a band until 1948, so they did not receive their black hackles until 1947.
In 1937, the London Irish Rifles extended the caubeen's wear to the entire regiment. In World War II, they were the only soldiers to wear the caubeen until 1944, when the 2nd battalion of the London Irish were serving with the Irish Brigade in Italy. The 2nd battalion of the Inniskilling Regiment started wearing caubeens made from Italian soldiers' greatcoats in January 1944, and the 6th battalion of their regiment soon copied them.
In February 1944, the British Army fortuitously made the "General Service" cap (a sort of oversized beret made from serge wool) the new standard undress cap. The caubeen passed muster, as the exact form of the GS cap hadn't been formalized at the time, and their re-tailoring of the stocks of GS caps went largely unnoticed by the ACI.
In 1947, the wearing of the caubeen was later extended to all of the infantry regiments in the post-war North Irish Brigade, with the Royal Ulster Rifles receiving a black hackle.
The Royal Irish Rangers (formed in 1968 by the amalgamation of the remaining regiments in the North Irish Brigade, The Royal Inniskilling Fusiliers, The Royal Ulster Rifles and The Royal Irish Fusiliers) were granted the wearing of the caubeen with the Irish Fusiliers' green hackle. It continues to be worn by the Royal Irish Regiment, created by the amalgamation of the Royal Irish Rangers and the Ulster Defence Regiment in 1992.
A blue caubeen, with hackle of three vertical stripes in colours matching the Royal Signals stable belt, is worn by officers, warrant officers and sergeants of the now disbanded 40 (Ulster) Signal Regiment. Sergeants wear an anodised metal Royal Signals cap badge, while officers and warrant officers wear an embroidered cap badge.
The modern caubeen is worn very high on the off-side (usually the left), which makes it resemble a tilted rimless Balmoral bonnet. It is often made with narrow black tapes, that are worn tied neatly in the back; the Canadian version is made with wide tapes. It is traditionally rifle green in colour, and typically worn with a unit insignia (sometimes worn with a short colored plume called a hackle, indicating regimental association) pinned on the off side of the cap.
Canadian and South African Army use
The caubeen remains the headdress for the 2nd Battalion, the Irish Regiment of Canada. It is a Primary Reserve light infantry regiment of the Canadian Forces. The Regiment was formed in Toronto, Ontario in 1915 as 1 Battalion Irish Regiment. The caubeen is worn with a green hackle, but not to designate it as a fusilier regiment as in the British Army sense; it was a gift from a commanding officer of the London Irish to the Irish Regiment of Canada during the battle of Coriano, Italy. The Regiment also wear an O'Saffron tartan kilt and scarlets. In the late '90s and early 2000s, the regimental dress was in slow decline, but more recently, the regiment has been re-issuing regimental dress at a steady pace.
In the past, the caubeen has been worn by members of the South African Irish Regiment, a Reserve Infantry battalion within the South African National Defence Force.
The caubeen is also worn by the honour guard of the Division One, Orange County, California branch of the Ancient Order of Hibernians, an Irish Catholic fraternal organization. On their website they remark: "And we wear the green caubeen and carry the pike, the distinctive headgear and weapon of the Irish warriors of old".
In 1938 the Irish Prime Minister's deputy, James Dillon, complained about a tax on imported ladies' hats, remarking that Irish ladies would be forced to wear "Connacht caubeens". In response a ladies'-hat factory in Galway declared that, when Dillon next visited the city, they would present him with a suitable "Galway caubeen".
Caubeens are also sold as a women's woolen winter hat by an Irish hat retailer.
The caubeen receives mention in the Irish song "The Wearing of the Green", of which the best-known version was written by Dion Boucicault for his 1864 play Arragh na Pogue, or the Wicklow Wedding, set in County Wicklow during the 1798 rebellion. The following is the second verse of Dion Boucicault's version:
When the law can stop the blades of grass
From growing as they grow,
And when the leaves in summer time
Their verdure dare not show,
Then I will change the colour
I wear in my caubeen,
But till that day I'll stick for aye
To wearing of the green.
An old song, still popular in Ireland, is "The Golden Jubilee" (or "Fifty Years Ago"), in which a wife exhorts her husband to take off his hat and put on his "ould caubeen", which he had worn fifty years previously. It was recorded by Connie Foley and Dorothy McManus in the 1940s and later by Sean Dunphy. 
- "caubeen". Oxford University Press.
- Terence Patrick Dolan: A Dictionary of Hiberno-English. Gill and MacMillan, Dublin. 1999. ISBN 071712942 X
- William Carleton: Willy Reilly, 1856, Chap. XIII, etc.
- Murphy, David (2007). Irish Regiments in the World Wars. Osprey Publishing. p. 56. ISBN 1-84603-015-3.
- "London Irish Rifles". Retrieved 23 January 2008.
- "The South African Irish Regiment: An Exemplar of the Military Traditions of the Irish in South Africa".
- "The Hibernian Guard of AOH Division One, Orange County, California". "We have adopted a uniform which acknowledges the present and hearkens back to our past. We wear a peasant shirt emblazoned with the modern day logo of the AOH. And we wear the green caubeen and carry the pike, the distinctive headgear and weapon of the Irish warriors of old."
- Irish Times, 7 April 1938, p. 8.
- Vance, Norman (2002). Irish Literature Since 1800. Pearson Education, pages 81–2. ISBN 0-582-49478-8
- "(Ireland) The Wearing of the Green". Retrieved 25 January 2011.
- The Golden Jubilee
- Report (6 April 1901). "RIC Meeting". The Irish Times. p. 15.