1890. While on watch in the engine room and steaming at a steady rate, the water level begins to decrease and suddenly drops out of sight in the boiler gage glass. Your FIRST corrective action should be to __________.

A sudden drop in water level indicates a potential low-water condition, requiring immediate action to prevent overheating and potential failure. Securing the fires is the priority to remove heat input and mitigate the risk of tube rupture or explosion.