A phalanx allows you to determine the arrival time for fleets destined for an enemy planet. One often uses this information to launch attacks against that enemy planet, timed to arrive two or three seconds after the phalanxed fleet arrives. A blind phalanx is a technique used to accomplish the same timing, without the use of a sensor phalanx, hence the 'blind' aspect. Timing, arithmetic, and luck are all key components in successfully implementing a blind phalanx, and the risks of failure are considerable.