Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

Right, I know the progression for Space Marines is Scout-Devastator-Assault-Tactical-Veteran (Blood Angels swap Assault and Devvie)
My question is, at what point does a Marine become a Sergeant? I would assume that they would be promoted to Sergeant after becoming a Veteran, but then is there another strand of promotion? Do they become Sergeants if they are the most experienced member of their squad, so they become a Scout Sergeant then a Devastator, then a Devastator Sergeant and so on? Do they chose what sort of squad they lead, are they assigned squads, do they start at Scout and work their way up?

Thanks in advance

The marine is promoted to Sgt by his captain. The captain assigns the new Sgt to a squad or promoted the marine from a squad memember to the leader of that squad. Scout Sgt are generally veterans and served as marines before. Every Sargeant is a veteran as the difference of Sargeant : veteran seargent has been dropped. Marines can advance to veteran status without becoming a seargent before.

Scout > marine.

Marine > Sgt

Sgt > captain

Captain > chapter master

So the Captain basically just selects an experienced marine and promotes him as and when he needs to?

Yes.
The Captain got his company to assign ranks as he see fit and the advice of the chaplain and any other marine he asks to suggest a person.

The sub-organizations however will pick candidates for their ranks too so a captain has to deal with the apothecarion, reclusiam and arsenal who will snuck marines from him...and the chapter master may request a marine for the 1st company too.
Experienced marines are a valuable resource and every group will lay its hands on a interesting candidate if they can.

Sergeants would be promoted based on potential for leadership. Exceptional Marines without leadership talent would eventually become Veterans.

Exceptional Marines with leadership potential and experience in the First Company are Veteran Sergeants even though the game has essentially removed the tabletop differentiation by giving all Sergeants 2 Attacks.

There's a hierarchy amongst the Sergeants too, because surely the Captain isn't present at every battle so there needs to be a chain of command so that senior Sergeants can become Commanders temporarily. Junior Marine officers (lieutenants) disappeared with 2nd Edition, but there had been differentiations between levels of Commanders in previous editions so that not every Space Marine force was commanded by a Captain. So it stands to reason that senior Sergeants take command in situations where the Company Commander is either out of action, or for detachments smaller than company size.