First, let’s look at the basic training regiment.
Officers goes through officer cadet course after basic military training. All in all, it takes 9 months to complete the course.
NCOs goes through specialist training after basic military training. That takes 6 months.
Others varies, depending on vocation and unit.
Great! If the service cuts off at 1 year mark, everyone will be happy!
However, after the basic training, there are other activities that reinforces the training. Some get shipped out to other countries for military exercises. Some stay put in camp, but applying what they are trained to do. As NSF, you get ingrained with what you have learned for the remainder of your active time. After you ORD and go through ICT, even though your first cycle might be rusty, but what you learnt and applied during your active days will not leave you. The subsequent cycles will be more fluid.
Additionally, the training schedule above excludes less than ideal cases of people who have to drop out of training due to reasons, or of people who went through BMT, then unit training where instructors discover and recommend them for further training for NCO role. It also does not cover additional training that one may have to take midway through the service.
Not only that, there is also some form of knowledge transfer from outgoing unit/personnel to the incoming unit/personnel (again, depends on your unit). These knowledge transfer are usually knowledge that is not by the book. (i.e. As a lance corporal that mans the hotline, requesting a whole section of soldiers stationed at a remote point of entry into camp to take up basic perimeter defence because of an incident prior to getting instructions from the officer (at his office) is not unheard of. This, you do not see it in the books). Before it was shortened to the current 2-year service, it was 2.5-year (or was it 2.25?) service. The extra time was used to do that. While I was active on the 2-year cycle, NSMen who did guard duty with me (as a RP on an airbase) could recall the time back when they could afford the luxury of x2 more time than now to “break-in” their juniors into the role that they are supposed to perform.
Logistically, shortening the time will reduce the manpower that each unit receive on a year to year basis. Understaffed units will be merged and there will be a point where there won’t be enough active personnel/units to react to emergency. Already, your meals, inventory, physical training have been outsourced to reduce the number of vocations so that the manpower can be better assigned other roles. Physical standards and classifications have been tweaked, along with adoption of technology, to beef up the strength of the combat fit personnel. Nonetheless, the crux of the problem is the declining numbers of teenage males enlisted due to the declining birth rate.
Some here have compared to the national services in Europe where it is much shorter. But do remember that these countries have armies that makes up of mostly professional soldiers, not conscripted soldiers. The closest comparison would be Israel, where it serves the interest of the country to have everyone know how to defend for themselves in event of gun-totting hostiles strolling down the boulevard.
If you want the service time to be shortened, correct the perception that professional soldier is a last career choice to take. Also be prepared to have a larger percentage of GDP taken out for defence purposes as the pay for a professional soldier will be much higher than that of an enlistee.