Blank machine gun fire rang out across Pearl Harbor on Friday as sailors on the submarines USS Charlotte and USS Missouri practiced firing from shore at an “attacking” small boat during the Navy’s “major force protection” exercise known as Citadel Protect.

Small boats are a low-tech but still potentially deadly force against U.S. ships at home or in a foreign port.

In 2000 two suicide bombers pulled alongside the USS Cole in a skiff while it was docked in Yemen for a fuel stop and detonated hundreds of pounds of explosives, blowing a huge hole in the side of the destroyer and killing 17 sailors and wounding 39 others.

Armed Iranian Revolutionary Guard Corps in small attack craft occasionally harass U.S. Navy warships in the Persian Gulf.

It’s important to reinforce to younger sailors that events like the USS Cole have happened before and that they need to practice against it, said Senior Chief Timothy Santel, a weapons instructor on the Charlotte.

“Bringing them out here and actually allowing them to shoot and operate the weapons kind of brings it home and says this is a thing that can happen. This is a thing that we need to train towards,” Santel said.

On Monday the crews of the Charlotte and cruiser USS Port Royal will defend against mock small-boat attacks while on their actual ships.

U.S. forces will additionally have to repel an “active shooter” attack during the exercise. “It’s another threat that sailors could face while guarding a ship, for instance, in port,” said Chuck Anthony, a spokesman for Joint Base Pearl Harbor-­Hickam.

Also being practiced is communications with harbor defenses. The two-week Citadel Protect started Monday and will end Friday, and already included harbor security boats taking on the threat of enemy small boats.

The result has been a lot of machine gun blank fire resounding across the joint base with the use of MILES (multiple integrated laser engagement system) gear to register hits and misses.

About 16 Charlotte crew members, seven from the Missouri and about nine from Submarine Squadron 1 were on a Hickam pier Friday for blank shooting practice with belt-fed Mk 48 machine guns.

A black rigid-hull inflatable boat served as the aggressor, weaving back and forth and heading straight on — always at a slow speed — as a target for the machine gun practice.

“A (live) round will give a splash in the water, and you can walk the rounds in,” Santel said. “This is to let them learn to train their weapons at a moving target — and then on the actual exercise they (the boats) will be coming in full bore.”

The sailors fired the machine gun in short bursts with the results coming back almost immediately over the radio. “Nine kills, one near miss” was one evaluation.

The exercise provides training for both underway and in port, Santel said.

“Mostly, this is going to be an in-port scenario where we’ll be tied up to the pier,” he said. “Basically, it’s how to defend the submarine best when we are in port. However, we have the same type of defense systems when we are underway and on the surface.”

The value of the Mk 48 machine gun training “is teaching other guys that have never used a gun or never touched a gun how to properly and safely use it — just in case we do need to use it in a real-life scenario,” said Fireman Manuel Julian, 21, a Charlotte crew member who teaches others how to use firearms.