In the discovered attack formation one piece opens the line for the other piece (line piece – queen, rook or bishop) of the same side. The line piece performs an attack or a threat to the enemy camp.
1.Rb6+ discovers the bishop check and the checkmate is unavoidable. Here the moved piece, that is the white rook, does not attack the enemy piece, but it controls the b-file which is crucial for mating net.
In some cases both of these pieces perform an attack on enemy piece, enemy king or a square.Then the discovered attack is a form of double attack and it is difficult to parry. Typical piece formation for a discovered attack is seen in the position from the game Zukertort-Blackburne. White queen and rook are on the same file as the black queen. At the moment, the bishop stands in the way, but if it moves, the line pieces will face each other.
1. Bg7! The bishop discovers the attack along the e-file, and at the same time it is checking the black king – double attack!
If the line piece checks the opposing king, this is discovered check. In following position, White moves his knight to open the diagonal for his queen.
1. Ne8+ Discovered check. Knight is also interfering the 8th rank and controlling the g7 square.
Sometimes both moved piece and the line piece give a check to the enemy king. This is known as double check. In such a case, checked king must move away, the check cannot be answered by interposing another piece or by taking the attacker. There is a famous example:
1. Qd8+ Decoying the black king into Discovered Attack! 1…Kd8 2. Bg5+. Double check and mate next move.
Discovered Attack examples: