"Like a Battleship, but with much less floating. Which means it’s even less likely to sink!"
Fortresses are a tier 8 Military industry. The price is 100 AA Battleships, 100 JJJ Bullets, and 4 Comrades. Fortresses are a large jump in comrades from the last 5 generators, and are a bit harder to reach and purchase than Coast Guards. While fortresses are still feasibly affordable with 131k bonus, at least 1 M comrades per second is recommended for the 160 B comrade unlock. Also, the Battleships cost will require level 2 Mega Tron and Level 5 Megacop (or equivalent - x10 M discount) to feasibly afford.