A Tam O'Shanter is flat cap distinguished by woollen ball on top of the cap
The woollen ball, mini pom-pom is also called a Toorie and adorns many Scottish military or Highland dress.
Originally a Tam O'shanter would have been made of wool and would lie much flatter than this one.
A Tam O'shanter is basically a beret with a pom-pom on top.
The khaki cap here (or similar) was introduced in 1915 for wear in the trenches by Scottish infantry serving on the Western Front. This came to be known as the 'Tam o' Shanter' later abbreviated to 'ToS' by the army.
