Easily comparable to assault, but with a bit of a twist on the mode. Several wings of the destructable walls guarding a primary objective. These walls are extremely well defended; mine launchers, artillery pieces large and small, the works. Those weapons platforms are your primary enemy, and the overarching objective is to penetrate the enemy's defenses to assault their "Fortress".
The catch to this is that it's on a time limit. If you don't manage to reach the fortress in 5 minutes, enemy reinforcements arrive, including the all loved (desperately hated) Titan vessel. These vessels would have to follow the path you took through the walls, but they would be dangerous if you've been lagging behind.
Limited lives, of course, and with multiple approach options to get to the heavily guarded fortress. A little difficult to simply speed run it, but it's certainly encouraged to try and beat the timer.