Ship Launching on 'You Tube'

When briefly surfing 'You Tube' I came across this ship launching footage, I never knew ships where launched in this way and thought others might find it interesting.

'You Tube' ships being launched
http://www.youtube.com/watch?NR=1&feature=endscreen&v=79HxuXP3D2w

The ice breaker I worked on in the Arctic