Okay kiddo, have you ever heard of a submarine? It's a big boat that can go underwater. Well, imagine if bad guys wanted to use a submarine to sneak illegal things like drugs from one place to another without anyone knowing. That's called a narco-submarine.
To make a narco-submarine, the bad guys have to be sneaky. They start by building a big metal tube that looks like a submarine, but smaller. Then they put an engine in it, like a car engine, and make it run really quiet so nobody can hear it.
The bad guys also put a special hatch on the top of the narco-submarine that they can open so they can put illegal things like drugs inside. They have to make sure the hatch is watertight, so no water gets in and ruins the drugs.
Once everything is ready, the bad guys get in the narco-submarine and start the engine. They drive it underwater, trying to avoid being seen by the police or military. Sometimes they even use GPS and other gadgets to help them stay hidden.
Finally, the narco-submarine reaches its destination and the bad guys open the hatch to get their illegal stuff out. Then they close the hatch, start the engine and drive back the way they came.
It's a very sneaky way to do bad things, and that's why narco-submarines are illegal. The police and military are always trying to catch the bad guys with their narco-submarines so they can stop the illegal things from happening.