The Combat Center is home to Glorious Expedition challenges. Construction requires Base level 16. The building has one level; advancement happens through battlefront missions and their difficulty levels.
How battlefronts work
Glorious Expedition has three battlefronts. Iron Phalanx recommends Infantry Heroes, Storm Wings recommends Aircraft Heroes, and Ironclad Barrier recommends Tank Heroes.
You select a difficulty for each battlefront during a challenge cycle. Once confirmed, that choice cannot be changed within the current cycle. Clearing all missions on the selected difficulty for the first time grants another opportunity, allowing at most two difficulties per cycle.
Heroes and mission progress
Each hero can participate in only one battlefront type per cycle. Assigning your strongest heroes to one front therefore affects which heroes remain available for the others.
Clearing missions grants items exchangeable in the shop. It can also grant a free level to a participating hero below level 100, without exceeding that hero's level cap. Unfinished progress resets when the next cycle begins.
The Infantry, Tank and Aircraft Center improve their corresponding hero types outside the challenge itself.