There were concrete blocks and steel beams sticking up from the ocean bottom like a sunken forest. Those were another method of preventing a landing. Your average giant fish or ship would tear a hole in its belly, but that did not work here. This enemy’s belly actually broke, smashed, and crushed the underwater obstacles.

Crowley’s Hazard.

No one had officially named them that, but it had naturally occurred to everyone in the 53 attacked countries.

It was not at all an even fight. Their opponents pushed back against the hail of cannon fire, blew away the ocean turrets and unmanned observation ships, and even cleared away the underwater obstacles in the shallows. They had already arrived that close.

Toaru Majutsu no Index New Testament vol.20 ch.1 pt.1