Rockets can of course launch underwater. Rocket engines do not take oxygen from the air. They either use stored liquid oxygen or another oxidizer or use a solid fuel that is self oxidizing. This is why there are so many videos of rockets launching from underwater. Not to mention the other ways using compressed air that were mentioned. Gunpowder is self oxidizing, this is why you can shoot guns underwater.
3. Sceptic once again shows how he knows nothing about anything.
20:18 onwards. You were saying about rockets?
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That agrees with what I and others have said. It does not agree with anything you said.
When the video claimed rockets can't work under water if was wrong. I'm sure the type of rocket they were showing in the video is too big to work underwater.
A video of an Estes Rocket launching underwater has already been posted.
Here's a video of a fighter jet launched from a submarine, so I guess it must be true. Don;t dare tell me that this is special effects.
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That video is fake on purpose. It even says it in the description. Like it says, it's just a jet put over a titan missile that was launched from the water. What evidence do you have that since one video was fake on purpose every single video is fake?
You don't say?

There may come a time when special effects and CGI will hit home in how your life is manipulated into accepting official lines by the use of this stuff.
Let me just put this nice and simple for you. You will deny this but I actually know for a fact this would happen.
Let's assume that the media puts out a story about the Armed forces testing out a new fighter jet. A new jet that can launch from under the water from a special submarine.
This naturally would get people like you wondering what this new jet is and will you ever see it.
A few years later after saturation coverage into your mind, they pull out the exact video of an official jet launch from a sub.
Naturally you are the rest of the ever willing people, wil, watch the video and stand back in total awe, excited about just how far we can go with technology like this.
I come along and tell you that the whole thing is one big fake. Giess what?
I am a tin foil hat conspiracy lunatic who knows nothing and that video is real. See what I'm getting at here?
If you want to read into the science that is clearly made up fantasy, that's absolutely fine...but if you are smart, you really should be questioning this stuff and trying to see it for what it really is, which is absolute gunk.