In the Greek system, reservists of arms like artillery and armour, stay in their arm's reserve for a few years and then get transfered to the infantry. I think I once read that artillerymen get transfered after 4 years. Which means that a conscript who served in artillery at age 19-20, by the time he gets 25 years old he is a reservist rifleman. I wouldn't be surprised if among reservist tank crews the time is even shorter. That's quite strange. You spend a lot of time and money to train up artillery and tank crewmen, and then turn them into infantry several years later? I imagine this is probably because you do not have enough artillery pieces and tanks to need so many crewmen? We have a similar system. We don't have that many tanks so we can replace the crews with new ones quite quickly. Once a sufficient number of new crews have been trained, the old ones are given new assignments in the reserve. For some it may mean transferring into a 2nd line infantry unit, whilst someone who has a degree in engineering will be placed in a pioneer slot somewhere. Officers might get put into staff jobs.