X-Ray Attack

The chess term "X-ray attack" is unusually precisely dated: it originates with American chess master and writer Kenneth Harkness, who introduced it in the April 1947 issue of Chess Review magazine, in his instructional series Picture Guide to Chess. Having just explained forks, Harkness identified a related but distinct double-attack pattern — two enemy pieces threatened in a single line, one behind the other — and, finding no good existing name for it, wrote: "This double threat has lacked a good descriptive name. We suggest 'X-Ray' attack." The metaphor draws on the medical imaging technology, itself only a few decades old at the time, in which X-rays pass through an obstructing body to reveal what lies behind it — precisely analogous to a piece's attacking or defending power passing conceptually through an intervening piece to reach a target beyond. The term has since broadened beyond Harkness's original double-attack sense to include certain defensive x-ray patterns as well.