LEARNING OBJECTIVES: Discuss the maintenance, prefire, and misfire requirements for current naval guns.

The power and complexity of the gun mounts we just examined call for a high degree of skill and knowledge on the part of the operator to ensure safe, efficient operation. Gun firing operations are very dynamic in nature. The operator must possess a thorough knowledge of the capabilities of the system to be effective. As mount captain, you will coordinate the actions of your gun crew while controlling the operation of the gun. This includes prefire inspections, gun loading and firing, changing ammunition types, down-loading, and post-fire cleanup. When casualties occur, you will also coordinate the troubleshooting and repair effort. If a casualty results in a misfire situation, you will supervise the crew in clearing the round from the gun. A misfire is the failure of a round of ammunition to fire after the initiating action. A hangfire is a firing delay beyond the normal ignition time after the initiating action. Because of the danger of a hangfire, you should always wait 30 seconds before opening the breech of a gun that has misfired.

A casualty situation involving a misfire is very dangerous. Having a hot gun further compounds the problem. A hot gun condition exists when the gun barrel temperature is raised sufficiently to cause the danger of ammunition cook off. Cook off occurs when some ammunition component (powder or projectile) reacts (burns or detonates) due to heat absorbed from the walls of the gun barrel. The exact procedure for clearing misfired rounds from the chamber of a gun varies from one gun to the next and will not be covered here. However, we will provide you with a general overview of some common elements in the procedure.

While firing, the mount captain monitors how many rounds have been fired and notifies his or her crew and CIC when a hot gun condition is reached. On a 5"/54 gun mount, this occurs after 50 rounds have been fired in 4 hours or less. When a misfire occurs, the mount captain notes the time of the misfire, makes additional attempts to fire using alternate firing circuits, and determines if the breechblock is closed. All of this information is passed to CIC and the gun crew. The mount captain then uses a safe clearing time predictor chart to determine if a lo-minute safe clearing time exists. The time duration of firing and the number of rounds fired are used to determine whether or not a lo-minute safe clearing time exists. If a lo-minute safe clearing time exists, the mount captain then requests permission from CIC to clear the gun according to the procedures prescribed in Clearing of Live Ammnition from Guns, SW300-BC-SAF-010. A cold gun is cleared one step at a time, with the mount captain getting permission from CIC for each step. However, after getting permission to clear the gun in a hot gun situation, the mount captain takes charge and carries out each step on his or her own authority while CIC monitors the situation.

It is useful to consider here that a misfire can be caused by a variety of casualties. Given the complex nature of modem gun systems, their firing circuits are designed to act as safety interlocks that prevent firing until all necessary conditions have been met. The round may be chambered and the breechblock closed, but if all the surrounding equipment is not in place with all the correct switches energized, the gun will not fire. A failed or misaligned switch, a sticking or misaligned latch mechanism, or a faulty control circuit component can cause a misfire. Misfires are caused by these types of casualties often more frequently than by faulty ammunition. While a misfire caused by a faulty powder charge is remedied by replacing it, electronic and mechanical casualties must be diagnosed and repaired before firing can resume. Verifying your equipment position and checking a few connections at the beginning of a misfire could save time in clearing that misfire. The problem could be as simple as the firing lead having come loose from the firing lock.

While clearing the gun, it must be kept on a safe fire bearing. This is to avoid accidentally hitting friendly forces when clearing the round through the muzzle. If the gun is hot, commence external cooling immediately. External cooling consists of attaching a fire hose to the barrel at the gun shield so that it sprays cool fire main water on the outside of the barrel around where the projectile is seated. Internal cooling can only be started after the propelling charge has been removed. Internal cooling uses a straight applicator that is inserted in the barrel to spray cooling water around the projectile. If the propelling charge is not removed and happens to cook off with the barrel full of water, the blast would demolish the gun.

The exact procedures for clearing misfired ammunition from guns used by the Navy, including small arms, are found in Clearing of Live Ammunition from Guns, SW300-BC-SAF-010. The information provided in this manual should not be used as a reference for actual operations.

SUMMARY

In this chapter we described gun positioning and ^{firing equipment.} We reviewed the gun systems currently in the fleet, focusing on their loading systems. In subsequent chapters we will describe how each of these systems is used with a fire control system, how the systems are aligned, and other maintenance requirements associated with guns. The chapter concluded with a discussion of gun operation and misfire procedures.