How did the caisson gate open on the Thompson drydock?

The caisson gate on the Thompson drydock opened through a system of buoyancy and counterweights. When the drydock was flooded, the caisson, which was sealed at the entrance, would float up slightly, allowing for the opening mechanism to be engaged. This process would typically involve releasing water from the drydock, lowering the water level, and allowing the gate to swing open. The design ensured that the caisson sealed tightly when submerged, preventing water from entering the drydock while it was in use.