SKETCH OF TRENCH SYSTEM] SECTION IV. Behind the support trenches the C. T. should be constructed on the traverse principle of _Section I_, so that the same defensive features existing for the support trenches as should exist for the firing line. In doing this, however, it should be kept in mind to provide rapid transit for troops behind these supporting lines. This is best done by continuing the zigzag system right through support trenches as shown. When necessary, this C. T. can be blocked. It is always a possibility that support trenches may be lost, but not a probability. Therefore, undue weight should not be given against the convenience of adopting as soon as possible again the zigzag C. T. of _Section II_, the latter supplying all requirements of rapid transit and allowing the introduction of straight stretches in loophole traverses wherever required. TELEPHONE LINES It is generally found that artillery telephone lines are laid on the north and west side of a C. T.; infantry lines on the south and east. Lines are generally laid about two feet from the bottom of the trench, picketed inter-grooves being cut into the side of the trench. These lines must be given absolutely every protection possible by the infantry and by any one using the trenches. Far too much carelessness has at times existed which destroyed communication with artillery and infantry when it was of vital importance that it should be open. Infantry in the trenches depend for immediate support upon their artillery, and if, through lack of supervision on the part of the officers in charge, these lines are destroyed or temporarily torn down by careless men not understanding their significance and importance, then that officer or officers is guilty of a very serious crime. RECESSES These are usually made in C. T. to allow for the passing of troops or bearers of stretchers, or parties passing up and down to the line carrying the many things that are necessary for the upkeep of that line. It is advisable that these should always be placed in the same corresponding place in each stretch, as shown in SECTION III, just before the turn, so that men know where they are to be found. The first man of a party coming up having arrived at a turn, and seen or heard others coming down, can give necessary protection to his party, and a great deal of unnecessary and very exasperating and fatiguing movements, and sometimes retracing of steps, is avoided. It is also often the cause of a great many casualties in a trench where these recesses are not made, as parties of men coming and going very often, while struggling to get past one another with their loads, are caught by heavy shell fire.