There were again no casualties and all the mines were planted. Two ships planted 710 each in continuous strings, fully establishing the success of the mining installations. There was no longer any doubt of the ability of one of these ships to plant her entire load of 860 mines without break. All vessels returned to base ready for further duty.
The explosions of defective mines on this excursion amounted to between 4 and 5 per cent, and reports received from British trawlers watching the first minefield indicated that enough more had gone off in that field since the first day, to bring the total there up to between 5 and 6 per cent. Despite all remedy, these explosions increased in number up to the 5th excursion. Then the cause was found to be due not to unskilful, negligent, or otherwise faulty procedure in either the ships or the bases, but to lie partly in supersensitiveness in the mines’ adjustment, partly in imperfection in manufacture—inevitable in such large numbers made under prevailing industrial conditions, especially of a new design.
On June 29, just before departure on the second excursion, the minelayers Shawmut, Captain W. T. Cluverius, Aroostook, Commander J. H. Tomb, and Saranac, Commander Sinclair Gannon, and the repair ship Black Hawk, Captain R. C. Bulmer, had arrived from the United States. Uncompleted work had not delayed them like the others, but the trial runs of the Shawmut and Aroostook showed their fuel consumption to be much larger than had been estimated—no data having been available when their conversion was planned—making their fuel capacity insufficient for the passage over. Indefinite delay, until a tanker could accompany them, was averted by the captains hunting up enough oil hose to fuel the ships at sea. Their departure on June 16 took place during the German submarines’ activity on the New England coast—not a favorable condition for ships just out of a navy yard. Twice during the crossing, the Black Hawk took the Shawmut and Aroostook in tow, to give them fuel oil. Though a new operation to all hands—likewise new ships, new crews, half a gale of wind, and oil hose twice as heavy as proper—it was done well, without mishap, and all four arrived at our bases ready for service.
The third excursion could therefore be made by the full squadron of ten. It was to continue the first minefield, and as some of our mark buoys were known to have broken adrift—we had passed two on the second excursion—the flagship’s navigator, Lieut. Commander Cunningham, was sent out in the squadron tugs Patuxent and Patapsco, to verify what might remain of the buoyfield. Finding half the buoys in place, he planted two new ones as a precaution. Then he passed along both our minefields, listening for further explosions, but heard none. The necessary improvement in the buoy moorings was now made, so effectively that they could be counted on thereafter. Each ship carried four buoys on her quarters, ready to drop on the instant. One stroke of an axe, or pull on a slip would release a buoy and its 1000-lb. sinker together, the mooring wire cable being so looped up around the buoy as to pay out clear. Thus the ship had no need to reduce speed nor any fear of getting her screw foul of the buoy.
Embarking mines for the third excursion had already begun when a message came that no mines were to be placed west of zero longitude for the present, a restriction that shortened the intended line by 30 miles, quite upsetting the embarking arrangements then in progress.
Meantime, the original plan had, in London, undergone considerable modification as to the constitution of the barrage. Originally of three systems, each comprising three lines of mines—upper, middle, and lower levels—the necessity which had developed for wider spacing between mines, to avoid structural damage to neighboring mines when one was detonated—300 feet instead of 150, as originally planned—made it seem desirable to increase the number of lines of mines, so as to maintain the same density of the mine barrage as a whole. The revision aimed to increase the risk to surface passage considerably. No effective patrol being maintained along the barrage, submarines would naturally prefer the surface. The revised plan, in brief, made 10 upper level rows instead of 3, and 4 middle and 4 lower level, instead of 3 each, or a total of 18 rows instead of 9.
Rather than shorten our line and again employ only part of the squadron, the Commander of the Mine Force took up the revised scheme at once, ordering 5400 mines prepared, for a field of 5 parallel lines 54 miles long. All 10 ships were loaded nearly to full capacity, Housatonic taking 840 mines. Departure was taken at 2 p.m., Sunday 14 July, hauling down, as we got underway, the dress bunting which had been hoisted in honor of the French Bastille Day.