I was watching ww2 in HD on Netflix last night and they said this guy who was a newly promoted corporal took control of his squad during a battle. How did they decide he was ready for a promotion and did they promote soldiers often? I have no experience with the army promotion system but it seems like it would be hard to track who they promoted and when.
First post on here so I may get some formatting wrong. I'm assuming you're talking about battlefield promotions. A battlefield promotion is when a soldier distinguishes himself in battle through leadership or technical excellence. It can be awarded up to the rank of staff sergeant. It was discontinued in the 70s but reinstated by the US military in 2009.
It also could be due to lacking manpower. If a corporal is doing the job of a sergeant because he got wounded or killed and doing a fine job, why would you bring in a new guy?
Citations:
Stephen J. Ochs (2012). A Cause Greater than Self: The Journey of Captain Michael J. Daly. Texas A&M University Press. p. 88.
You can also read about battlefield promotions on Wikipedia. I'm also in the Canadian Army which is where some of the knowledge comes from just from the environment I'm in.
Assuming you are referring to the US Military, very rapidly. I will do a comparison to today, since until very recently I was an active duty army officer. In the military, succession of command would dictate who is next in line, it generally works off rank, position and tenure (generally referred to as years in service.) These days, because we have lower casualty rates, we don't see a lot of corporals who may be in charge of say, a platoon (this wasn't uncommon in the pacific during WWII) However, promotions under a certain rank can usually be handled by a Battalion which would track it through its personnel section (in the army known as the S-1.) And yes, Soldiers in WWII were promoted very rapidly to fill positions which would be vacated by someone killed or wounded. Take Dick Winters (one of the main characters in band of brothers.) Dick Winters on the eve of D-Day was a 1st Lieutenant. His company commander was killed and being the most senior Lieutenant filled the billet and eventually the accompanying promotion to Captain(2 weeks later), so overnight he skipped what today would take a minimum of 18 months from date of promotion to next rank. After 8 months, he was promoted to Major, a promotion which takes a minimum of 4 years in todays army. As to keeping track of who was promoted when, there was likely to be accompanying paperwork of sorts, the movies/documentaries would never discuss this of course, because who wants to watch a guy fill out a form for 5 minutes.