Found this snippet a good read
http://www.gavinrothery.com/my-blog/2011/9/23/spaceships-that-became-other-spaceships-1-the-millennium-fal.html
http://www.gavinrothery.com/my-blog/2011/9/23/spaceships-that-became-other-spaceships-1-the-millennium-fal.html