I recently came across this question "What decides who goes in the front rank in a line infantry formation?" and while trying to form an answer to it I realised I was making the assumption that the sizing of a formation in modern foot drill, like many modern drill commands, has its origins in the 1700s/1800s.
It is common (I am hesitant to say this always happens as it has been a while since I did any drill) for a squad to be sized as part of the process of forming a squad in marching order. AP818 (The drill manual of the RAF) states:
The reason this movement is taught is that a correctly sized squad drills betters together and gives a better impression to the spectator.
Stating that a correctly sized squad drills better together is hard to prove, but I can see how it would related to large line formations as used in the Napoleonic era as effective drill was vital.
So, my question is: What are the origins of sizing a squad in modern foot drill? or Does the practice of sizing a squad in modern foot drill originate from Napoleonic Era drill? It's worth noting I'm not necessarily looking for an date or an era but I am unable to find much information on the origins of modern foot drill.
Note: While I refer to "a squad" this method is also used to size a flight, which is a subdivision of a Squadron. Also, this command is (in my experience) common across the RAF, RN and Army.
Note: This post mostly relates to the British Army (with reference to the RAF drill manual - which is based on the Army's drill manual), but is likely to be common across several nations armed forces for this time period. So answers referring to Commonwealth Nations, the USA, France and Germany (to name a few) may be relevant.
Info on squad sizing
Sizing a squad results with the tallest members to the left and right hand sized of a squad, with the shortest in the middle.