anterior aircraft-carrier formation=前出航母编队

deploying aircraft-carrier formation

把南沙打造成不沉的航母，可以大量储备军需物质，作为{前出}航母编队的中途后勤基地，战时也可以进驻大量战机对南海周边国家形成威慑，
The Nansha Islands could be turned into a "fixed aircraft carrier". Large stores of military supplies would be placed there, and it would serve as a forward support area for aircraft carrier battle units leaving on missions. In times of war, large numbers of fighters could be based at Nansha to ensure air superiority over the surrounding countries.

Debouching just means that troops and equipment are going out into action. It does not necessarily mean that the troops are at the front or the vanguard. So this sentence is describing using the islands as logistics bases for debouched aircraft carrier formations. That's the term I use in technical translations, but it is not a word most people use every day.