Can an 11B switch over to become an 11C? If so, what are the requirements?

I’m guessing you’ve done all that yourself already?

11B and 11C and when there was a 11H were MOS in the same job family and about 60% the same. 40% of the training was different though and....
Approx 40% of the time 11B would concentrate on squad drills, tactics and patrolling.
Approx 40% of the time 11C would concentrate on mortar gunnery, placement, etc.
Approx 40% of the time 11H would concentrate on enemy tank ID, TOW firing drills, emplacement, tactics, etc. So what inevitably happens is a 11B will look over and see what 11C's do and say hey I like that better. The problem with 11H is we would not road march as much as 11B's but instead drove because the TOW was so heavy we had a TOW gun jeep or TOW Hummer........so that was an attraction to the 11B's that were tired of marching everywhere. Some liked the idea of driving better than walking. 11C's some like firing explosives more than firing a weapon. So thats why the switching of MOS.......that and being Infantry it really gets monotonous training to do the same thing every single day, for months and years (it has to be that way though), and some people just get bored but not bored enough to leave the MOS. 60% of the time each of the three MOS did the exact same thing.

Sir, in some cases the more training and MOS/SMOS/AMOS you have makes your more marketable to the unit and gives you more avenues for promotion, I did OJT for the 11C and 11H MOS in my day and I enjoyed the training. I also have a couple of MOS's that made it slightly easier for promotions hen things slowed down in one MOS. In the end it is all dependent on whats good for the Army. The higher in rank you get the less chance you will be allowed to re-class. Also down the line if Big Army has a shortage of one of your MOS's then you could get a suprise order to transfer to a unit in need.