Remember, also, that though you may arrange matters so that you cannot be enfiladed by rifle-fire, yet you may be open to it from long range, by means of gun or pompom fire. There are few straight trenches that cannot be enfiladed from somewhere, if the enemy can only get there. You can sometimes prevent being enfiladed by so placing your trench that no one can get into prolongation of it to fire down it, or you can "wiggle" it about in many ways, so that it is not straight, or make "traverses" across it, or dig separate trenches for every two or three men.
14. Do not have your trench near rising ground over which you cannot see, and which you cannot hold.
15. Do not huddle all your men together in a small trench like sheep in a pen. Give them air.
16. As once before—cover from sight is often worth more than cover from bullets.
For close shooting from a non-concealed trench, head cover with loopholes is an advantage. This should be bullet-proof and not be conspicuously on the top of the parapet, so as to draw fire, or it will be far more dangerous than having none.
17. To surprise the enemy is a great advantage.
18. If you wish to obtain this advantage, conceal your position. Though for promotion it may be sound to advertise your position, for defence it is not.
19. To test the concealment or otherwise of your position, look at it from the enemy's point of view.