When you pack as many people as possible into a mini van, with enough weed as you can get and all start smoking at once. the ratio of people to smoking paraphernalia should 2:1, but more joints, bowls, bongs, and hookahs never hurts. The point of the submarine is not to be moving but to find a safe spot and fish bowl it so bad that you take a hit just by taking a breath and make it hard to see in from the out side from all the smoke.
Side note: Always remember to bring food and drinks in the van before you start smoking
the smoke was so thick when we went submarineing last weekend, that you literally couldn't see your hand one foot in front of your face