It's not relevant to the thread and I'm sorry for being picky but you wouldn't call them 12th or 24th Squadron, it's twelve or twentyfour Squadron.
Being an ex RAF type myself it's just one of my pet peeves. I know that's how the Americans call their squadrons so it's understandable and you do see it quite often but it's always irritated me.
Don't mean to offend.
Understand what you mean. The difference originates from the fact that the USAF (and its forebears) always put the definite article (ie "the") in front of unit designations (eg "the 1st Fighter Wing) - and "the" is always implied even if not actually present in the actual sentence.
For those who may be unaware of the origin of RAF naming conventions, the following may be of interest. Instead of the definite article, the RAF uses the word "number" which, again, can be silent if the word isn't actually present in the sentence (eg "I served on 13 Sqn from 1992-1994" is essentially saying "I served on
number 13 Sqn from 1992-1994"). The RAF convention was drawn from the preceding Royal Flying Corps (RFC) which, in turn, grabbed it from the cavalry.
In the British Army, the main unit organization is the Regiment and the definite article is employed for such formations (eg "the 21st Lancers") because they are uniquely identified. Since subordinate units are not unique, it is inappropriate to use the definite article because there may be many sub-units all with the same designation. This is where the cavalry linkage comes in. Cavalry sub-units are squadrons, usually identified by a letter or a number (eg "A Squadron" or "number 3 Squadron"). The definite article is not employed because of the risk of confusion (there being several "3 Squadron" entities across all the Army's cavalry regiments) and because you can't have "the Ath Squadron"! When the RFC was formed, it was decided to use Squadrons as the primary unit organisation, and the cavalry-based naming convention stuck. Nowadays, we tend not to insert the word "number" into the description and simply refer to the unit as, for example, "13 Squadron".
As an additional bonus, the Royal Navy also used the term "squadron" to define a formation of vessels. The use of the squadron as a formation dates back to at least the early 19th Century and is still in use today for small groups of ships (actually, that's pretty much all the RN can manage these days...). Just to be confusing, the RN did use the definite article but, since the RAF was proportionately made up of more RFC units than RNAS units, the Junior Service (ie the RAF) stuck with the Army convention.
All entirely logical and justifiable, really...!