Double attacks with the rook are simple enough to understand, but they also are easily overlooked because the rook is used so heavily for other more familiar purposes. The suitable targets for a rook fork are the enemy king, the enemy queen (if the rook has protection), or any loose piece. As a practical matter the targets of a rook fork almost always include either the king, a loose piece, or both; this will be the guiding principle behind our target-based searching. The visual pattern involved also can be stated simply: a rook can slide between two pieces on the same rank or two pieces on the same file. The first pattern is more common; in the skeletal diagram to the left, White’s rook has forked Black’s king and bishop. The other type of fork—the double attack against pieces on the same file—occurs less often and can be a bit harder to see because the rook then moves into the forking position horizontally. The eye is more accustomed to tracing the rook’s path up and down the board, rather than from side to side.
Another factor sometimes making rook forks harder to see is that the enemy targets may begin with other pieces between them—yours, his, or both—that have to be cleared out of the way before the fork can work. The solution to all these difficulties is to be habitual and thorough in looking for enemy pieces on the same rank or file, just as you are in looking for pieces on the same diagonal—and this regardless of whether there are other pieces between them. The principle is general: when you look at lines on the board and pieces resting on them, follow all the way through. Don’t let your eyes stop when they hit an obstacle, because the obstacle may be removable through an exchange or by other means; if there are two enemy pieces on the same line, you want to see that pattern every time regardless of what lies between them.
Occasions for double attacks by a rook arise less often than forks with the other pieces we have considered, and there are only a few special wrinkles that rooks present. This chapter therefore is shorter than the previous ones.