The double cannon (双炮) checkmate position does not come up too often in games, but is still important to learn, as it can be used in conjunction with other pieces to secure a checkmate.
The diagram below demonstrates the how powerful the double cannon can be. The circled cannon places black's general in check. Neither of black's elephants, nor black's advisers can prevent check, as placing them between the general and the two cannons would cause the other uncircled cannon to threaten black's general.
This second diagram below demonstrates how a beginning player can end up being checkmated by double cannons if he or she is not careful.
The above game is a bit like the Scholar's Mate in international chess, where checkmate is easily preventable. This last diagram below demonstrates how: