For as long as their have been professional police and firemen in the United States, it has been common for many of these men to also belong to the military reserves (or National Guard.) The police and firemen rarely have the same job in the military, but when a lot of reserve units are mobilized, many police and fire departments find themselves seriously short of personnel. Many departments don't even know how many of their people are in the reserves until there is a major call up, and suddenly they have lost ten percent or more of their staff. This has been particularly difficult for smaller police and fire departments (those with fewer than a hundred members.) The solutions have ranged from canceling vacations and making overtime mandatory, to bringing back recently retired members of the force until the emergency is over.