This week my letter will be a short one, as it only contains one very simple problem. You are on outpost duty and have been told that the General is very anxious to get one or two live prisoners. Your picquet is at some cross-roads a quarter of a mile south of the road _A B_ marked on the map. You have reason to believe that it is probable that the enemy will patrol down the road _A B_. _A B_ is a good road with strong fences on either side of it, and with ditches on the road side of the fence. Does any special way of taking prisoners alive in this road suggest itself to you? _Solution._ A very good plan to adopt in these circumstances would be what the Japanese used to call the trap-door. If your post consists of six men, leave four under the leader at _A_ and tell them to conceal themselves in the ditch, and place two, also concealed in the ditch, forty yards in front of the mat _B_. If the enemy’s patrol comes along, the men at _B_ should allow it to pass them and then give a signal and at the same time themselves take steps to cut off the patrol’s retreat, whilst the four men at _A_ prevent it advancing farther. * * * * * The above little scheme is so simple that I should feel that I ought to apologise for setting it, were it not that I am quite certain that three out of four of your comrades to whom you may set it will not give the proper solution. I saw a similar little problem given to men of different regiments in India. The only troops who answered it properly were Pathans. It apparently much resembles traps which they set for one another in their inter-tribal fights. Although some twenty teams competed, neither British troops, Sikhs, Hindustani, Mohammedans, nor Rajputs ever managed to successfully catch their men. Your affectionate father, “X. Y. Z.” LETTER X [Illustration] _February 7, 1918._ PROBLEM 10 MY DEAR DICK,-- The problem I am setting you to-day has to do with fire control. You are on outpost facing in a northerly direction and are in command of a picquet consisting of the headquarters of a platoon with a Lewis gun and thirty men at _G_. A man who has been sent in from a group on your left tells you that a company of the enemy is moving across your front from left to right along the road _A B C D E F_. He says that the company is marching with an advanced guard of one platoon about 200 yards in front of it. The platoon has a couple of groups 200 yards in front of it again. Five minutes after you have received this notice, you see a group of the enemy marching from the wood at _B_. _Problem._ How do you appreciate the situation and what action do you intend to take? _Solution._