Attention had, from the start of the tunnelling scheme, been directed to the subterranean parts of Kaserne B. Kaserne A had, for the purposes of a tunnel, been ruled out for various reasons. For one thing, the personnel of the working-party as originally constituted belonged almost exclusively to Kaserne B. For another, Kaserne B was in itself the building more favourably placed geographically for such an attempt. Kaserne A was for half its length Kommandantur; its “business end” was out of reach for the English. Accordingly, the basement corridor of Kaserne B was studied in all its aspects. It will be remembered that this floor contained the detention cells and the various cellars, that it was entered at each end of the building through a door at the bottom of a short flight of steps, and that half way down the corridor itself were two doors usually locked. It will be clear, perhaps, that the business end of the building from the escape point of view was bound to be the far end, and that the best base of operations would be somewhere underground in the vicinity of the orderlies’ entrance. Owing to the near presence of the detention cells and the consequent risk of meeting the gaoler at awkward moments it would be useless to enter the corridor at the officers’ end. It would be necessary to make acquaintance with the underworld by going in the first instance through the orderlies’ entrance. Thence some part of the basement floor might be penetrated, either through the door at the bottom of the steps, or by some other means—to be explained shortly. The door I have mentioned was used only by the Germans and was kept locked. It might be possible to tamper with this lock, but it would have to be done from the outside, at the foot of the staircase. These points have been laboured, but it is highly essential for it to be understood at the start that the only possible entry to the potential base of operations—except by breaking down the barricade or by burrowing at some point through the reinforced concrete of the actual masonry of the building (a process which would greatly imperil discovery)—lay, in the first instance, through the orderlies’ entrance. I have explained that there was a short flight of steps leading down to the basement floor. This was on the right as you passed the threshold of the entrance door. On the left was the first flight of the staircase leading up to the baggage rooms and orderlies’ quarters. To the left of the steps down, and completely blocking up the underneath part of the first flight up, was a palisade of stout upright planks, each about six inches across, a further Boche precaution against undue communication with the cellars. [Illustration: A. Section, B. Ground-plan of staircase, chamber, and tunnel entrance. ]