Caubeen The caubeen is a bonnet that originated in the twentieth century after being adopted as the headdress of a number of units of the British and Commonwealth armies , where its formal name is the " Bonnet , Irish , Green " . Name . 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 " . According to the " Regimental Catechism " of " The Irish Regiment of Canada " , it is suggested that the name " caubeen " may have been derived from the French word " corbeau " , referring to the dark - green colours given to the bonnet by the French , for whom many Irish soldiers fought as mercenaries over the centuries . However , it is also stated in the Regimental Catechism that it is " more likely " derived from the Irish word " caipin " " ( sic : cáibín ) " meaning " old hat " . Military Use . British Army . 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 . Other usage . 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 . In song . 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 . Another Irish song referring to the caubeen is " My Old White Caubeen " , which the Irish Times reported was sung at a meeting of the RIC in 1901 .