Siege

Once more the cannonballs flew threw the air, though this time there were undoubtedly less of them. Feeling confident because of the ineffectuality of the last volley, many of the soldiers either took a single step back, or took refuge within the fortifications of the tunnel.

But Matsudaira squinted, and recognised the difference in the magnitude of these projectiles, and immediately gave the order. "CLEAR OUT FROM THE TUNNELS IMMEDIETELY!"

With the speed with which they were hurling towards the earth, they did not have much time to scramble up the dirt slope, and get in the clear. The unfortunate were trapped inside as the heavy ball slammed into the earth. 

With the depth of the tunnel, and the measly foundations, the beams soon sported cracks due to the immense force that was sent coursing through them, and after a terrible groan, and a look of despair, they gave way, dropping tonnes of earth onto the defenceless soldiers underneath.