...why units are disbanded, rather than just changing role? By which I mean, if an infantry unit is 'surplus to requirements', why can't it be re-roled as (for example) 3rd (Transport) Battalion, the Royal Anglian Regiment, or 4th (Signals) Battalion, the Royal Green Jackets, etc. The Guards had tank battalions in WWII, and there are Yeomanry signals and arty units. Is it just empire-building on the part of the RLC and other corps? I can't see any logical reason why, in the course of a 400-year history, a regiment can't be pikemen, tankies, truckers and machine-gunners.