What tool is commonly used for securing a watertight door?

The tool commonly used for securing a watertight door is referred to as a dog system or latch. This is because a dog system consists of various locking mechanisms that operate to ensure a watertight seal is maintained when the door is closed. The design allows for the efficient engagement and disengagement of the door, making it suitable for environments where maintaining a water-tight barrier is critical, such as in ships or submarines.

This system typically includes dogs (or latches) that can be engaged around the perimeter of the door, pressing it snugly against the frame to prevent water ingress. The effectiveness of a dog system can be attributed to its ability to evenly distribute pressure along the seal, ensuring operational reliability under different conditions. Thus, the dog system or latch mechanism is essential for ensuring the door's integrity, especially during flooding or emergency situations, making it the correct choice.