In some countries, you are able to participate in a game of chance to decide your military service length.
In TH a1 l A |\| D for example, if not enough people voluntarily join, they'll hold a lottery.
The length of service will then be determined by pulling a card. If it's a red card, you'll need to serve. If it's black, you're free to go. If you volunteered, your service is much shorter than what it would be if you participated in the lottery.
If you have a degree and volunteer, you serve just 6 months. If you pulled a red card, you'd serve a year.
No bachelor + volunteer = 1 year
High school diploma + red card = 2 years
No high school diploma + volunteer = 2 years
The ratio of red cards to black cards depends heavily on how many people volunteered.
People with mental issues, females and ladyboys are exempt.