To have a solution, you must have a problem. In a Naval context, the Fire Control Solution, is the answer to the question “How do you hit a moving target, through a moving medium, from a moving platform?”
It is a simple question that is often very difficult to answer. Imagine that you are standing in a field, and you are tossing a baseball back and forth with a friend. It is your job to throw the ball to him. It is quite simple when he is standing still. It becomes more complicated when he is running in a straight line. More complicated when you’re running in a different direction. More complicated when he starts zig-zagging. More complicated when he runs behind a tree. More complicated when the ground starts shifting back and forth, and you still need to hit him.
Calculation of the fire control solution depends first and foremost upon knowledge of how the weapon system that you are using behaves. Tossing a baseball back and forth is very different from tossing a sandbag, football, or a feather. Firing a shell from a gun at an aircraft is very different from launching an active radar-guided missile at a ship, which is very different from firing a passive radar guided missile at an incoming missile. I’ll go into a bit more detail on each of these examples later.
Another thing that you need to know is where the target is, and what it is doing. Not only do you need to know where someone is, and how fast they are moving, but also how they are moving. It’s useless to know that someone is 20 meters from you, and is running at 2 meters per second, if you don’t realize that they’re also running in a big circle. If you toss a ball at them based on just where they were and how fast they were going, by the time the ball gets to them, they will have turned and the ball will miss them. So, we need to use our sensors (primarily radar) to determine where the target is relative to us, and what they are doing. There are complex algorithms that are used to determine the target’s speed and acceleration, as well as attempting to predict future course or speed changes.
The types of radars used for tasks like this are called, naturally, fire control radars. Instead of your typical search radar, which transmits a wide beam, and continuously scans the entire horizon, a fire control radar is designed to transmit a very thin “pencil beam”, and once locked onto a target, will continue to follow that target. The thinness of the beam allows the radar system to very precisely calculate the position of the target. Fire control systems will, if needed, also be outfitted with the capability to “illuminate” the target, by sending out a continuous transmission of electromagnetic radiation at a particular frequency. This energy hits the target, and acts like a spotlight, allowing other radar receivers tuned to that frequency to notice the target. It is this energy that allows passive radar guided missiles to home upon the target, with the obvious caveat that while the missile is in flight towards the target, the ship that is illuminating the target must continue to do so. Otherwise, the missile will lose all its information about where it is supposed to be going, and likely rather quickly crash into the sea.
The next thing that you must know in order to find the fire control solution is how you are moving. If you want to be able to point your gun at something, it really helps to know exactly how your ship is rocking with the waves. Imagine you are attempting to fire upon a helicopter that is hovering above the water. If you did not know how your ship was moving, as you bounce through the waves, your sensors would likely be telling you that the helicopter is oscillating up and down in altitude. Instead, what is actually happening is that your ship is rocking back and forth, while your radar continues to look straight at the motionless helicopter.
In order to correct for this, you need information from components of the ship’s navigation system. Every warship is equipped with a set of accelerometers and gyroscopes. These systems measure the ship’s heading (Where the bow of the ship is pointed), the roll (How much the ship is tilted about the axis from bow to stern), and pitch (How much the ship is tilted about the axis from port to starboard), as well as how much the ship is moving back and forth, up and down, to port and starboard.
The next component of the Fire Control Problem is the moving medium. The wind speed and direction will have an effect upon the path of any projectile that you are trying to launch from your ship to the target. So, you use anemometers to measure the wind. As the brighter ones out there have already realized, you need to take what you measure, and subtract from it your own ship’s speed and course, which you measured in the last step, in order to calculate the true wind speed and direction.
So, now you should have all the information needed to calculate the Fire Control Solution! When dealing with a missile, the calculation that needs to be done on the ship is a lot simpler. All the missile needs to know is where it needs to start looking for the target. For a passive radar guided missile, this consists only of what direction it needs to “kick over” to, after launch. For the active radar guided missiles, you also need to tell them how far they have to go to start looking for the target. These missiles, such as the Boeing Harpoon missile, are typically rather “smart”, with the ability to program them to navigate around islands, other friendly ships, and various other waypoints, before they turn on their radar seekers and start looking for the target. They even have the ability to launch multiple missiles, and program them to simultaneously attack a single target from multiple directions, reducing the likelihood that the target will be able to shoot down all missiles that are inbound.
Calculating the fire control solution for a gun system, on the other hand, requires far greater precision, as unlike a missile, the shell being fired does not have the capability to correct its aim while in flight. Typically, this is an iterative process. The processor responsible for the calculation of the fire control solution will first calculate what direction the gun needs to be pointed to hit the target where it is at that point in time. Then, it will figure out how much the target will move during the time of flight of the projectile. Then, it calculates where the gun needs to be pointed in order to hit this new position, recalculates the time of flight, recalculates based on the targets movement during this time. It then repeats this process until the difference between subsequent calculations is suitably small. While the target is being tracked, it continuously performs this process, waiting for the command to fire. Thus, when the fire button is presses, the gun will already be pointed such that the projectile and the target will both be moving into the same space at the same time.
Obviously, these calculations do not leave much room for error, and requires very precise measurements of all the parameters mentioned above, as well as detailed information on the ballistic characteristics of the shell, such as its muzzle velocity, and its coefficient of drag. All of this would be measured by the system’s manufacturer.
While I have mentioned frequently that all these calculations are very complicated, and require high degrees of precision, as I’m sure that you can imagine, you do not exactly have time to pull out your abacus when there is an Exocet missile inbound at Mach 0.9. The pace of Naval warfare is ever increasing, with a ship’s captain possibly only having seconds between the time that a missile is detected, to when the button to shoot it down had better have been pressed. So, needless to say, modern warships are jam packed with loads of complex computers that can automate these processes, even allowing the ship to perform the “detect to engage sequence” without any human intervention. Typically, ships do not sail around in that particular mode of operation, as humans are still a lot better at determining whether or not it’s a good idea to shoot at something than any computer is.
And, while this writeup is focused on the wonderful world of above water warfare, this type of process also needs to be performed for our friends who live under the waves. Torpedoes typically work rather similar to a active radar guided missile. You point it in the right direction, set the initial search depth, and let it go. You need to have an idea of where to send it, typically receiving target location information from some type of sonar. After you launch, the torpedo will turn on its own sonar and use it to, hopefully, home in on the target. The fire control solution is calculated in the same way, just with different inputs.