(H) Loop-holed tunnel. Length 162 metres; inclination 60 per cent.; elevation gained 83·50 metres in this tunnel itself, or a total of 168·50 from the second dump. This tunnel (the one through which the men were to pass for the attack after the explosion of the mine) had to be strictly confined to the rocky stratum between the Tofana and the Castelletto; its planimetry appears (see map), therefore, rather uneven due to the constant elevation of the rock. (I) Line of communication--partly in a natural cavern--measuring about 250 metres in length and giving access from the lodging quarters to the works. (J) Tunnel dug out to the extreme south end of the Castelletto, 30 metres long, with two portholes (each 4 metres wide) for two Depfort guns, with closed cavern for the guns and ammunition. “It was originally intended to divide the explosive charge between two chambers, each having a mining line of resistance of 20 metres, with a 16-ton explosive charge of 92 per cent. gelatine. However, owing to the countermining work carried on by the enemy--we were only a few metres from one of his positions during the charging of the mine chamber--we were obliged to confine the entire charge to a single chamber. “The enemy meanwhile, with a view to avoiding the effects of our mine beneath the peaks of the Castelletto, had transferred most of his shelters to the side of the Tofana and the Selletta. This necessitated a considerable alteration in the location of the mine as originally planned, in order that it should act against the enemy shelters on both the Castelletto and Tofana flanks. [Illustration: PLAN OF THE CASTELLETTO MINING OPERATION. The worm-like tunnel on the left had to be driven in this way in order to avoid fissures in the rock which would have revealed what was going on. It was this tunnel through which the Alpini were to pass to occupy the crater after the explosion of the mine, but this plan was defeated through the presence of gas from detonated Austrian asphyxiating bombs.] “The charge was computed on a basis of minimum resistance of 20 metres, taking into consideration the nature of the rock (which was fissured) and the existence of numerous splits and caverns. The co-efficient of overcharge was, therefore, rather high. In order to obtain the maximum effect under these conditions, only 92 per cent. explosive nitro-glycerine was used. The total charge was 35 tons.