Hackle

The hackle is a clipped feather plume that is attached to a military headdress.

In the British Army and the armies of some Commonwealth countries, the hackle is worn by some infantry regiments, especially those designated as fusilier regiments and those with Scottish and Northern Irish origins. The colour of the hackle varies from regiment to regiment.

The modern hackle has its origins in a much longer plume, originally referred to by its Scots name, heckle, which was commonly attached to the feather bonnet worn by Highland regiments (now usually only worn by drummers, pipers and bandsmen). The smaller version originated in a regimental emblem adopted by the 42nd Royal Highland Regiment, to be worn in the sun helmet issued in hot-weather postings from the 1870s.

In the modern British Army, there is a single regiment of fusiliers, plus a battalion of a large regiment. Hackle colours are:

Other ranks of the Royal Welsh; the regiment that was formed by the amalgamation of the Royal Welch Fusiliers and Royal Regiment of Wales, continue to wear the white hackle of the Royal Welch Fusiliers.

There were several other fusilier regiments which have been amalgamated and no longer exist. The hackle colours worn were as follows:

Non-fusilier regiments which wear the hackle are:

Following the amalgamation of the regiments of the Scottish Division to form The Royal Regiment of Scotland on 28 March 2006, the following hackles are being worn by the regiment's constituent battalions:

...
Wikipedia