“This countersign is the recognition signal that Lieutenant Hunt asked about. It may be given by word of mouth. It may consist of whistling a few bars of some familiar service call. It may be made by tapping with the knuckles on the stock of the rifle. The number of taps to represent a number, for example: The countersign or recognition signal is 22-33. Corporal Canes would approach the sentinel post and strike his rifle, tap, tap (pause) tap, tap. The sentinel will answer in the same manner tap, tap, tap (pause), tap, tap, tap. He would then know that he had been recognized as a friend and proceed to the post. If the sentinel discovered Corporal Canes first he would keep him under observation and when he is close enough to hear would challenge him, tap, tap (pause), tap, tap. Corporal Cane’s answer would be tap, tap, tap (pause), tap, tap, tap. The system is interchangeable. The first number may be said to be the challenge or inquiry signal and the second number the recognition. “It is not well, however, to confine ourselves to any one set of signals or method of identification. They should be changed frequently, so that the enemy will never know what system is being used on any particular night. “When the countersign is a word it should be spoken in a very low tone of voice for fear of betraying it to the enemy’s scouts who may be near by. History is replete with incidents of disaster to covering detachments arising from the enemy’s knowledge of the countersign.” Solution _The Director_: “Now, Lieutenant Hunt, let us assume that you are at the sentinel post and ready to make your inspection. Just what would you say to him?” _Lieutenant Hunt_: “Well, sir, I am free to confess that I do not know just what I would say, but I would make a stab at something.” _The Director_: “That is just the point. Our text-books are here deficient again. They assume that this is so simple that we just naturally know what to do and what to say. Have you ever seen in any text book, any where, detailed instructions as to just how to inspect a sentinel on post. They say: ‘The officer of the day will inspect.’ I should like for you to be in a concealed position and hear some ‘Officer of the day’ make his inspection of a sentinel. Try it sometime and see the results.