Notice how right around the mark you pointed out scepti...........your question about water flooding into the tube is answered.
Of course it's answered. I mean, they have to provide the reason don't they, or their ruse is immediately ripped apart.
If you watch the video a little bit further back, they even try to cover for the heavier so called ballistic missiles by pretending the fire their rockets into some water to create steam that pushed the missile out. It's complete and absolute baloney, seriously.
I ask any rational person to question this stuff.
Next time anyone goes in the bath, get a bar of soap and pull it under the water near the bottom, then squeeze that soap as hard as you can to try and get it to jump out of the water.
The best you will do is pop it to the top and that's it.
Do people seriously believe that compressed air in a pipe can propel a 20 plus foot fully fueled missile up through 120 feet of water to pop out of the sea, then fire a rocket engine to go and hit a target.
It's stuff of fantasy. It's made for TV bull crap to have us all believing that nobody is safe at any distance.