The arming of traders gave the Central Powers furiously to think, especially as the policy was a perfectly natural sequel to their own misdoings. Details of the calibre of guns mounted by ships of the British Mercantile Marine were withheld from Parliament as “not in the public interest.” The French Minister of Marine was more communicative. At the end of 1917 every French merchantman was armed with two 3.7–in. guns. International law held that trading vessels during war-time must be stopped and searched before further action could be taken. Exceptional circumstances alone justified the sinking even of an enemy vessel, the usual practice being to conduct the captive to port, the final disposal being settled in the Prize Court. Neutral ships could in no circumstances be destroyed. Germany’s difficulty was that it was next to impossible for a submarine to follow this programme, which she herself had recognized previous to the advent of the U-boat. While the process of search was going on, a necessarily slow and tedious task, ten to one a patrol boat would appear on the scene and show an untoward amount of inquisitiveness. The natural development of blockade by submarine was _via_ the line of least resistance. Rules and rights, obligations and understandings must go by the board. The word illegitimate was wiped out. From naval virtue to piracy is but a step; the enemy took it. She would sink at sight. As a direct consequence of the arming of merchantmen there was an increase in the number of submerged attacks and a decrease in the use of the gun on the part of the submarine. This was entirely to the good, because it necessitated more frequent visits to the base to replenish depleted magazines. Elsewhere I have dealt at length with the wonderful way in which the men of the Merchant Service settled down to the altered condition of affairs.[33] The crews showed as much faith in their solitary weapon mounted in the stern as a gun-layer of the _Queen Elizabeth_ believed in the giant organs of destruction housed in the fore turret. They achieved wonders with the little spitfires, though sometimes their confidence was misplaced. Uncertainty is the only certainty in war.