The minelaying now runs entirely by the time table. Each ship gives her successor five minutes warning and, as her last mine dives overboard, shows the signal “Begin minelaying at once; I have suspended.” The successor begins accordingly, showing her red flag. The staff officers on board the San Francisco watch for these signals, comparing the times with what they should be, and counting also the seconds elapsed between the launching of successive mines, from the ships whose sterns we can see. A few seconds out now and then—otherwise all goes according to schedule, just as planned before leaving the United States.
The hardest task is on board the Housatonic—a new ship, with a new mining installation, of type untried in service, and a crew inexperienced in minelaying—dropping 675 mines without intermission, 1 every 11½ seconds, during 2 hours and 10 minutes. Her mate is standing by, ready for any interruption, but the Housatonic completes the task without a break—making a world record, a continuous line of mines, 28 miles long. On a later occasion, the Canonicus planted 860 mines in 3 hours 35 minutes, an unbroken line of 43 miles.
About 20 minutes after planting began, an explosion was felt and a geyser seen astern. A few minutes later the same occurred again, and other explosions followed, at varying intervals and distances, some just visible on the horizon. Others which were nearer, as evidenced by the sharpness of the shock, threw up no geyser, indicating that they were at the middle or lowest depth.
In the proof tests held off Cape Ann in April, it had been observed that a mine at the middle level, 160 feet submergence, made no surface disturbance when detonated, until 8 seconds had elapsed, and then only as much as the wash of a light swell over a submerged rock. At the deepest level, 240 feet submergence, a detonation produced no more surface upheaval than there is in a glass of well iced champagne. The ship being about 800 yards away, the shock was heavy and sharp. The water surface all over could be seen to tremble with the shock, but directly over the mine itself, when, after 27 seconds, the gas came up, there was no more surface disturbance than a pleasure canoe could have ridden with safety. A slick on the water would follow, but this could not be distinguished at much over a mile distance nor at all if there were a white cap sea running.
Observers recorded the number, times, and approximate positions of all explosions and, on board the San Francisco and Baltimore, there were listeners stationed at the submarine signal receivers, so as to get a full count. All observers did not agree, as the indications from sounds and shocks varied according to distance and depth. Some explosions gave a prolonged reverberation, at times sounding to the unassisted ear like two or three explosions in rapid succession, but in the submarine signal receiver each explosion made a distinct sound, unmistakable.
The count by the San Francisco and Baltimore, differing by only 2, practically agreed on 100 explosions, or about 3 per cent of all mines planted. Although a perfect record was desirable, the detonations showed the minefield to be alive and sensitive, and their number was not large for a new mine, not yet long enough in service to refine out the minor defects.
Surprising enough on deck, where one could see, that first explosion must have startled the men in the engine room, in the coal bunkers, and on the lower mine decks. The blow rings sharper down there, where resulting damage, in broken pipe joints or started boiler tubes, might be expected first. Whether gun, torpedo, or mine, however, it is all one—the duties go on just the same.
As the mines on the launching deck move slowly aft, those on lower decks move forward, to the elevators and up. Working spaces are cramped, passages narrow, bulkhead doors closed wherever possible. At the right time, a door will be opened, the portable section of mine track adjusted, the mines in that compartment hauled out, and the door closed again water-tight, all as quickly as possible. Close, hot, foul with oily steam and seasickness—it is sweating, disagreeable work below decks. But complaint is nowhere in the ships. The feeling is well expressed by one man, writing home:
When the first mine went over, I had a curious feeling of exultation. The fear, the perils, the uncertainties that surround our work, slipped from me like the foolish fancies of a nightmare. There, at last, was a nail in the Kaiser’s coffin. Come what might, I had justified my existence. Had the whole German High Seas Fleet appeared in the offing, I am sure I should have gone to my battle station with a shout of glee.