Answer:
Where humans breathe liquid.
Come up and we go, Go down and we stay.
If you drop me I'm sure to crack. But give me a smile and I'll always smile back.
What is the word that even in plain sight remains hidden?
They are the group who manages the winged engines of war.
I never sleep yet sometimes I weep. I can get angry or just be happy. Wherever you go, I will follow. No matter what you do, I will be there. I cannot die. What am I?