I googled sonic boom and found an article on the subject. It is quite good and easy to understand. Among other things it explains that the sonic boom only happens as an aircraft hits the exact speed of sound. However, at the end af the article, this proclamation is made:
"Our ships are beyond the speed of your supersonic planes, from the moment they determine to move. Its as simple as that, we skip the sonic boom period."
Then I saw it was from ZetaTalk.com:-)