18 months service by age 25. Service can be done in two separate installments of 9 months. It could be satisfied by participating in any of a list of activities approved by Congress. Such a list might include: military service, public works projects, UN relief agency work, religious missionary service, Peace Corps, Habitat for Humanity, tutoring in K-12 schools. Such work must include 40 hours of labor per week, but need not preclude participation in other activities.
The government would provide some basic stipend to those participating in a subset of the projects that are deemed to be directly beneficial to the country. Other options, such as religious service, would not receive a stipend but would satisfy the requirement.
This isn't really that different from the draft, it just allows more ways for people to serve outside of a military capacity.
Someone like Connor might argue that this program would amount to involuntary servitude which is prohibited by the 13th amendment. I would disagree, however, siding with the Supreme Court which wrote on this subject saying that the 13th amendment,
certainly was not intended to interdict enforcement of those duties which individuals owe to the state, such as services in the army, militia, on the jury, etc. The great purpose in view was liberty under the protection of effective government, not the destruction of the latter by depriving it of essential powers.
No, I'm not totally sold on the idea of mandatory national service. And I'm not sure what the penalties should be for violation or whether people ought to be able to pay a fee to escape the service. But I must admit that I am at least intrigued by the idea.