The first peacetime draft in US history was implemented in 1940. Congress renewed it (by a single vote) in 1941. The term of enlistment for draftees was 1 year.

When war broke out, those already in uniform found their term of enlistment was instantly set to "for the duration (of the war) plus 6 months", even if they were set to be discharged on December 8, 1941.

Stop Loss orders mean that individuals whose normal term of service is about to expire are retained in service. Most people who separate from the military are set to some form of reserve status. Effectively, Stop Loss means they're retained in service until the crisis is over.

This isn't the first time Stop Loss orders have been implemented. I'm pretty sure they were implemented in the months leading up to the Gulf War back in 1990-91.