ı had questioned something ı had seen on a blog that said the area defended by a Phalanx was 1200 square meters . If that had been the area described by the r=1200 in the equation , ı would have no problems . Even if the 155mm shells or 122 mm rockets are smaller than anti-ship missiles , the 1200 sqm figure would probably mean only the area the weapon trailer was positioned . In that case why not sand bags ? They are probably far cheaper .