PQ 18's cruising formation placed the merchant ships inside a screen of destroyers, corvettes, and trawlers. The escorts sought to create a cordon of protective fire and ASDIC detection around the convoy. Building enough ships and trained crews for this system took time, so early-war convoys could not all receive protection on the same scale. The formation makes the material cost of convoy defence visible before the more distant covering forces are counted.
Notable Point · 17:25-18:40
PQ 18 and the cost of a full convoy screen
PQ 18's close screen shows how many destroyers, corvettes, and trawlers were needed to surround merchant ships with detection and protective fire.