"Moves like a rook but can jump over a single intervening piece in a straight line, capturing the first enemy piece in its path."
Special Moves:
Siege Capture: "When a Siege Tower captures a piece, it also captures the intervening piece (friendly or enemy) in its path."
Examples of how the Siege Tower moves:
When the Siege Tower captures a the Queen, it also captures the intervening piece in its path, in this case white's Knight. Since the Siege tower must leap over a piece to capture, it's unable to take the Rook.
Black makes the move STd3, placing white's King in check via the Siege Capture rule, as the Siege Tower captures the intervening piece too. Had white's Bishop not been there, the King would've been safe.
Black's King is unable to move to d4, d5, or d6 due to the Siege Capture rule, as white's Siege Tower captures the intervening piece. If black's Knight wasn't there, it would've been safe for the King to cross.