In the previous chapter I mentioned that the explosion of the submarine took place shortly after the storming of the Mole had commenced.
The immediate purpose in destroying the railway viaduct connecting the Mole to the mainland was twofold: firstly, that of preventing the Germans from sending reënforcements across to the help of the Mole garrison; secondly, that of augmenting the main diversion. There were, however, ulterior objects also. Firstly, the destruction in itself would be a valuable part of the general work of demolition designed to reduce the efficiency of the Mole as a naval and aerial base; secondly, the loss of the railway would deny to the enemy the use of the Mole as a place of embarkation for military purposes. If deprived of railway communication the Mole would lose a high percentage of its special war value.
Two old submarines, C1, commanded by Lieutenant Aubrey C. Newbold, and C3, commanded by Lieutenant Richard D. Sandford, were chosen for the purpose—each carrying a volunteer crew of one officer and four men in addition to the officer in command.
The submarines were provided with special control apparatus so that the personnel, after having set the apparatus to guide the vessel to its destination, could abandon their craft before reaching the viaduct itself.
For the purpose of abandonment each submarine was given motor-driven skiffs and special ladders. The latter might enable the crews to climb up the viaduct and escape before the explosion took place, the motor skiffs being supplied for escaping to seaward if that was found to be feasible.
Each submarine carried a heavy cargo of high explosive. This latter was fitted with time fuses and special instruments so that there would be sufficient delay between the ignition of the fuse and the final explosion. At a prearranged minute after passing position G, the submarines were to have slipped from their towing hawsers and then to have made the best of their way to the viaduct. Unfortunately C1 was so much delayed by the parting of a hawser that she could not continue her voyage to the viaduct without running the risk of hampering C3. The latter, exactly in accordance with the Plan, slipped from tow and proceeded under her own engines on the prearranged courses. At midnight the submarine appears to have been sighted in the light of a star shell. Searchlights immediately picked her up and some firing was seen in their direction. Artificial smoke was immediately made use of, but the wind, having then commenced to blow towards the north, was found to be unfavourable. The firing was only of short duration and the artificial smoke was switched off. A few minutes later the viaduct showed up clearly against a glare in the background and course was altered to ensure striking exactly at right angles. Sandford disdained to use the control apparatus to take his submarine into her position.
The vessel was run under the viaduct, at a speed of nearly ten knots, immediately between two of the vertical piles. She charged against the horizontal and diagonal girders with such force as to penetrate the framework of the viaduct as far as her own conning tower, whilst being lifted bodily about a couple of feet on the frames. Firmly wedged under the railway in a position about fifty yards from the northern end of the viaduct the first part of the operation was completed. It is difficult to account for the small opposition offered to her approach by the enemy. Possibly they mistook her for a friend. Another suggestion is that they thought she was endeavouring to pass under the viaduct en route to the canal, and that, knowing this was impossible, they hoped to capture her intact. That suggestion sounds extremely unlikely. Possibly the diversion caused by our efforts at the other end of the Mole had distracted the attention of the defence commanders; the men may have feared to take unexpected measures on their own responsibility. Whatever the reason for the lack of enemy opposition, there was certainly no lack of difficulty. The darkness, suddenly giving way to the blinding glare of searchlights, the navigational difficulties, and the necessary care in handling such an awkward vessel combined to make their arrival a very fine feat. But finer was to follow.
Destruction of the Viaduct
Several of the enemy had appeared on the viaduct and commenced to fire on her with machine-guns from close range; the latter cannot have amounted to many feet! The crew lowered a motor skiff and Sandford ordered them to abandon ship. He then fired the time fuse and jumped into the boat. Their purpose was now to steam away to the westward at utmost speed so as to get well clear before the explosion took place. Unfortunately the skiff's engine was useless—the propeller had been broken! Oars had been provided for such an emergency and the crew pulled away from the viaduct for dear life. As soon as the boat was clear of the viaduct itself, the firing became intense, both from the viaduct and from the shore. The German searchlights were directed on to the boat.