There are unions involved. Union contracts usually make it very difficult to just "reassign" employees and backfill with new hires, especially if it involves different job descriptions, skill sets, working conditions & pay scales. If the employees involved don't want to move, most contracts won't allow managers to force them, either.
There is no quick fix if the problem requires a significant increase in MS staff. If the extra demand is thought to be temporary, most managers will not want to increase staffing. They'll use mandatory OT & other "bandaids" to tough it out.