I have already said that a great part of the destroyer's duty was to rescue merchantmen that were being attacked by submarines: this _Luckenback_ incident vividly illustrates this point. Had the submarine used its torpedo upon this vessel, it probably would have disposed of it summarily; but it was the part of wisdom for the submarine to economize in these weapons because they were so expensive and so comparatively scarce, and to use its guns whenever the opportunity offered. The _Luckenback_ was armed, but the fact that the submarine's guns easily outranged hers made her armament useless. Thus all the German had to do in this case was to keep away at a safe distance and bombard the merchantman. The U-boat had been doing this for more than three hours when the destroyer reached the scene of operations; evidently the marksmanship was poor, for out of a great many shots fired by the submarine only about a dozen had hit the vessel. The _Luckenback_ was on fire, a shell having set aflame her cargo of cotton; certain parts of the machinery had been damaged, but, in the main, the vessel was intact. The submarine was always heroic enough when it came to shelling defenceless merchantmen, but the appearance of a destroyer anywhere in her neighbourhood made her resort to the one secure road to safety--diving for protection. The _Nicholson_ immediately trained her guns on the U-boat, which, on the second shot, disappeared under the water. The destroyer despatched men to the disabled vessel, the fire was extinguished, necessary repairs to the machinery were made, and in a few hours the _Luckenback_ had become a member of the convoy.