Hey, kiddo! Do you know what a submarine is? It's kind of like a big metal underwater boat that can go really deep under the water.
Well, some submarines have a specially shaped tank called a "saddle tank." It looks like it's sitting on top of the submarine, like a saddle sitting on top of a horse.
The saddle tank is used to hold extra fuel for the submarine. You know how your toy car needs gas to go? Well, a submarine needs fuel too, and sometimes it needs to travel really far or stay underwater for a long time. That's when the saddle tank comes in handy because it can hold extra fuel to make sure the submarine can keep going for a long time.
But the saddle tank also does something really important for the submarine. You see, when a submarine dives down into the water, the weight of the water around it makes it harder to move. The saddle tank helps balance out the weight of the submarine so it can move more easily through the water. It's kind of like when you ride a bike and you lean to one side or the other to balance yourself.
So, in summary, a saddle tank is a tank on top of a submarine that holds extra fuel and helps balance the weight of the submarine when it's diving underwater. Isn't that cool?