Okay kiddo, let me try to explain what defense clandestine service is. Imagine you have a secret agent in movies who goes on secret missions to protect their country. The defense clandestine service is kind of like that, but for the United States of America.
It's a group of people who work for the government and their job is to gather information and intelligence from other countries, especially the ones that might be causing trouble for America. They need to be very sneaky and keep everything they do a secret, even from their own families and friends.
These people work in different parts of the world, pretending to be normal people, but secretly working to find out what others are planning. They work with other agencies like the CIA and FBI, but they focus on military and defense intelligence.
Their work is really important because it helps the government make important decisions and protect the country from any possible threats. But they need to be careful because if they get caught, it could be really dangerous for them and their mission could fail.
So in a nutshell, defense clandestine service is a group of secret agents who gather information and intelligence to protect the country, but they need to keep everything they do a secret to succeed.