the USA has it (but dormant as it was last used in the 60s) now, instead part of an automatic register.

The US doesn’t — and has never had — mandatory peacetime service of the “one serves six months or a year or something like that to be trained in military stuff during peacetime”, but if one is male, one does need to register so that in the event of a war where people are called up, one does need to serve then.

It also means that the US has to train people from scratch in a war where it needs them, so has a relatively-long time until it can greatly ramp up its forces if it needed them.