Tunnel

"Sir? A tunnel?"

"Yes sergeant. Dismissed."

The soldier came to attention and strode out the door, confusion marking his brow. The old man behind the desk unbuttoned his jacket slowly, and pushed his gray hair back from his forehead. This siege had gone on too long, too many lives lost and forever changed by the charges and fire of the enemies defences. To many soldiers died on the battlefield, opening their helmets for a last breath of Earth's good air, sullied though it was by innumerable toxins and contaminates.

The enemy had prepared well for this battle. Their food supplies and solar cells would last long, just how long no one could say. This battle needed to end, and swiftly.

The walls of the city were strong. True iron covered by an impressive array of generated force fields. Scanners of all kinds and missile defences that were the best in the world watched the skies ceaselessly. The Elite Infantry fought constantly and never seemed to tire. Drones and AI made circuit after circuit of the city, until their tracks made trenches in the dust.

But there was a weakness. There's always a weakness.

The rules of war had gone to far and left behind too much. A tunnel, dug swiftly and silently, far beneath the city walls, filled with the best troops and breached at precisely the right point.

The general smiled to himself, just a little bit. It would work, he felt it in his bones.