The United States has some 176,000 military reservists on active duty. Some 64 percent of America's 863,000 reservists belong to the army. At present, 20 percent of American military reservists are on active duty. But 27 percent of army reservists are on active duty, while only eight percent of air force, three percent of navy and 13 percent of marine reservists are. The "reserve system" was developed in the 19th century as a way to provide additional troops for a major war. The system was used, with success, in both World Wars. But times, and needs, have changed. Conscription, which provided a steady supply of trained soldiers to enter the reserve units, has become very unpopular. So now reserve units are largely filled with people who are recruited directly into the reserves. The rest are people who had served in the regular forces as a volunteer, and now are willing to do it part time.
But the 19th century reservists got paid little as conscripts, and less as reservists. It was considered a patriotic duty to serve. But without conscription, you have to offer competitive pay. The U.S. does that, and many people join the reserves because it's a good part time job. While all these reservists are aware of the small print (getting called to active duty for up to a year, or more, at a time), this never scared a lot of reservists off. For one thing, full time military pay is, for most reservists, was more than they made in their civilian jobs. And there are laws (not always enforced) that assure them of getting their civilian jobs when they come off an extended tour of active duty.
But there are thousands of reservists, particularly army reservists, who were not ready for an extended tour of active duty. These were small business owners, single parents or people with health problems they kept quiet (or didn't know about) that made them ineligible for active duty (or staying in the reserves.) Because of the Afghanistan and Iraq experience, all the services are rethinking how they recruit, organize and use their reserves. This is no longer a force just for mobilizing altogether and staying on active duty until a major war is over. No, the future is somewhere else. But no one has quite figured out what the reserve forces of the 21st century should be long. But the experience in Afghanistan and Iraq is being watched closely, as is the long term reaction of the reservists to the kind of service the reserve system was never really designed for.