There are two fish in a tank. One turns to the other and says, “You man the guns, I’ll drive”.
Answer: If you have a fish at home, it is in a tank: a fish tank (also called an aquarium). Normally when you hear about a tank and fish, you think of a fish tank. A fish tank is a glass box that holds water and fish.
The other type of tank is a military tank. If you are in a military tank, someone has to drive it, like the fish in the joke.
This joke is funny because the word tank has two meanings: a fish tank and a military tank. This joke misdirects us to start thinking of a fish tank when actually the fish are in a military tank.