Why did bushell want the prisoners to dig tunnels so deep?

Bushell was a key figure in the planning of the famous prisoner escape from the Stalag Luft III camp during World War II, which is best known as "The Great Escape." He wanted the prisoners to dig tunnels deep for several strategic reasons:

1. Avoid Detection: The deeper the tunnels, the less likely they were to be detected by the guards. Surface noise and vibrations from activities within the camp could more easily betray shallower tunnels. Deep tunnels reduced the chance that guards would hear digging sounds.

2. Escape Ground Microphones: The German guards used ground microphones to listen for the sounds of digging. Tunnels that were deeper were less likely to be picked up by these microphones.

3. Maintain Structural Integrity: Deeper tunnels were less prone to collapses. The pressure from the surface was more evenly distributed, and there was less risk of cave-ins from surface activities or environmental factors.

4. Bypass Security Measures: The camp had seismograph equipment and other countermeasures designed to detect shallow digging. By digging deeper, the escapees aimed to circumvent these measures.

The intended depth of the tunnels in The Great Escape was about 30 feet below the surface, to achieve these objectives and maximize the chances of a successful escape without detection.