What is the primary duty of the first engine at a boat fire incident?

The primary duty of the first engine at a boat fire incident is to spot on the gangway with the hose bed facing the incident. This positioning allows for rapid deployment of hose lines to attack the fire effectively. By placing the engine in this orientation, firefighters can quickly access the hose and respond to the fire's location without unnecessary delay. It also provides logistical advantages for securing a water supply and coordinating further actions with other responding units.

The other options, while important in various contexts, do not directly align with the immediate operational tactics required in this situation. Laying a supply line is crucial but typically follows the initial setup for direct fire attack. Establishing unified command is essential for managing larger incidents but is not the primary focus for the first engine at this phase. Searching for missing persons is critical in a comprehensive rescue operation but also takes place after the immediate fire control strategies are in place.