Have you ever been a Navy shipboard fire fighter? If they were spraying the hull they were doing what they were supposed to do. Fire on a ship {any ship} has a fast heat transfer rate to adjoining compartments. Too minimize that transfer so the fire simply by that heat transfer doesn't cause more fire in other spaces you do compartmental cooling off all adjoin spaces you can reach. It is standard U.S. Navy fire fighting protocol.
Fires can start from many non negligent causes. One of the more common is electrical where you either get a loose connection which will not trip breakers or fuses but heat to extremes or frayed or damaged cable unseen to the eye.
A fire on a ship can be hard to detect and isolated to a small space for hours under the right conditions where oxygen is low like in the insulation as one guy talks about. Once it burns through enough where it reaches sufficent oxygen then it's Katey bar the door.
Nobody on a ship wants a fire in any venue in port or at sea. Fire is the most feared and serious event short of coming under direct attack.
I spent a total of nine months of my four years on ship assigned solely to the ships Fire Department doing nothing but fire fighting. One of the worse fires we fought started in the shipyard. It was a storeroom fire and the heat transfer within minutes had climbed two decks up too the crew barber shop. The deck in the barber shop was so hot the floor tiles were bubbling. We flooded the deck.
The most annoying fires happened the night after Field Day when swabs used for waxing floors had not been properly rinsed out and after being placed in a locker caught fire by spontaneous combustion. But a Class C {electrical} fire can very quickly become a class Alpha fire by igniting other objects.
The larger ships like carriers back in about 1980 went to a full time onboard fire department for both at sea and in port. It made much better sense to pool persons from each department of the ship and train them for fire fighters than the old protocol which was to let the Hull Techs do it all which could in a bad fire take most of them out.
My son is a ‘glow worm’ on an LA class sub, and I remember him saying he’s a Fireman.
Most common fire when I was on a boat was a clothes dryer fire, cause by the combination of not cleaning out the lint, and the user not allowing the dryer to finish it’s cycle (the last 5 minutes of the cycle allows the dryer to cool down).
On a submarine, everybody trains as a firefighter.