Paid young adult mandatory military training/service is an entirely reasonable policy where if pay is high enough, enough old people will force the young to do it. Even mandatory “go die in vietnam because domino theory will destroy capitalism” can have more old people force the young into draft. Though obviously, exposing those reasons to kill our youth makes the vote less favourable.

If such an amount of people knows about our military strategy, so does the Russia.

Our military slave numbers are public.

The extreme cost of maintaining offensive and diminishment operations is the first thing likely to be eliminated in favour of cash dividends to voters. There can be constititutional limits on what can never be voted against. Legitimate defensive needs/preparation of the nation would be covered. Funding a proxy war on Russia or Palestine or Israel would come from personal individual donations rather than forced social budget support. Constitutional limits against offensive war propaganda are just as important as defense preparation.

Maybe there could be a restricted set of representatives that are allowed to vote in case we are attacked

There needs to be an administrator (President) to respond quickly to emergencies. Review of adminstrator behaviour after emergencies is a liquid democracy process. You’re right that genuinely required secrets (as opposed to frequent national security classified corruption and evil) would require private judicial review, but liquid democracy would select the judges.