Cannons are used in Association Croquet when three balls are in contact with each other. The main purpose is to bring all three balls into play in useful positions with a single stroke. Although cannons can be played anywhere on the lawn, the most common situation is when a ball is roqueted into a corner that is already occupied by another live ball. This is described as a Corner Cannon and the correct shot depends on which hoop the striker is trying to run next. The buttons on the left of this screen indicate the corner that the balls are in and the hoop that is to be approached. In each of the illustrations, "S" is the striker's ball, "C" is the ball from which the striker is taking croquet and "R" is the ball that is roqueted in the cannon stroke. The Corner Cannon is well worth practising for the improving player. If the opponent hides in a corner the striker has great difficulty promoting both balls into positions for use in a break and a corner cannon is often the only way. The procedure is to place the ball that has been croqueted (C) in its correct position on a yard line and touching the ball already there. The striker's ball (S) is then placed touching 'C'. The third ball,which is to be roqueted (R), becomes a ball in hand and is placed touching 'C' but not touching 'S'. 'S' is then struck along the line shown and roquets 'R' immediately. It doesn't matter if 'S' goes off the lawn as it has made a roquet before doing so.