The barrage began to show results early in July, after our second excursion, although not yet half across. The enemy submarines changed their route then, so as to go through Fair Island Channel, south instead of north of the Shetlands. Thus they would pass west of the partial barrage, through the 60-mile wide passage still open. The fact of Area A having been proclaimed gave ample warning, and even the enemy could not complain of being ambushed, if he sustained damage there. Advertising a minefield two months in advance was certainly fair play. But now came the mining of Area B, which would carry the barrier clear across the last 45 miles of the 230-mile stretch. This was not published, but the enemy might have assumed that it would be done sooner or later.
A joint excursion by the two squadrons was arranged, Rear Admiral Strauss commanding the whole, flying his flag on board San Francisco again. The squadrons joined off the middle Orkneys the morning of 7 September, and began the minelaying a few miles to the northward, starting from a buoy placed by H.M.S. Laburnum and removed by her after we had passed. As we were directly in the submarines’ thoroughfare, special patrols were provided, surface and air, in Fair Island Channel and also well to the southward of us. The American squadron planted six upper level lines, the British squadron planted one similar line, after the completion of which it separated to the southward, returning to its base at Grangemouth, Firth of Forth. On the way, one of them had a collision in the fog with a destroyer of its escort, which later sank in consequence.
Our squadron turned north at the end of our minefield, ran taut wire to Buoy No. 5, thence paralleled the minefield at five miles distance for observation of defective mine explosions, steering west to the Orkneys and returning to the base on the reverse of the outbound courses. Fog came on soon after mining was finished, continuing intermittently until we made port. For this reason, San Francisco did not cut her taut wire at Buoy 5 but kept it running until the squadron slowed to take in paravanes, near Cromarty—122 miles of wire run out, without a break.
The succeeding excursion was similar, with Rear Admiral L. Clinton-Baker, R.N., in H.M.S. Princess Margaret, in command of the whole force, Rear Admiral Strauss again on board San Francisco. On the way out, it was not permitted to pass between the Orkneys and the western end of the minefield planted just previously, but instead, the squadrons were routed NW’ly, through Stronsay and Westray Firths, in the Orkneys, thence E’ly through Fair Island Channel, and down to within five miles north of the other minefield.
While standing through Stronsay Firth in a long, single column, the British squadron, which was in the lead, opened fire on its starboard quarter, its escorting destroyers gathering to drop bombs about a certain spot. Upon signal from the Princess Margaret, the starboard wing destroyers of our escort speeded ahead to join the attack, but the port wing destroyers remained on station, although the leading squadron’s destroyers had left theirs. In a few moments, a submarine broached about 1500 yards, two points on San Francisco’s starboard bow, heading across to port, through the column, between the two squadrons. Some destroyers followed and continued bombing. Smoke screens were laid by our escort (Vampire, Captain Godfrey, and 11 others of 14th Flotilla) and by our own ships, which thus had a good test for their smoke outfits. Roanoke chanced to have a steering engine disablement just at this moment, causing her to sheer out and shift to hand gear, and the Housatonic also had some steering trouble, but there was no mishap, and the submarine also for the time escaped. By good luck, an official photographer happened to be on board San Francisco, and he got some pictures of genuine activity.
A delay at the morning rendezvous, the long distance round about, and adverse current combined to make a late mining start. While the mining was in progress, the bodies of two German sailors were passed, and a heavy explosion was observed in the eighth minefield, five miles distant, in a position that plotted in the same place a submarine would be which had been reported shortly before.
Darkness shut in about an hour before planting was completed but it caused no suspension nor interference. At the end of the field, buoys were dropped as usual, and all ships together turned left, without signal but on orders given before dark, to the course north, then formed in two columns for the run home. The British and American squadrons had now separated and they passed back through Westray Firth in succession after daylight next morning. Off Pentland Skerries a suspicious craft ahead caused another submarine alarm, and the escort again enveloped the squadron in a smoke screen, but the alarm proved false.
This time, the 10 American vessels had planted six lines, two at each of the usual levels, 46 miles long, 5520 mines in all, the maximum of any excursion; the 4 British vessels planted one line at deep level, 1300 mines, 32 miles long, making altogether 6820 mines on the excursion, the largest single minefield ever planted—done in 3 hours and 50 minutes. Upon returning to the bases, Admiral Strauss signaled “The Commander Mine Force congratulates the squadron on this biggest and most successful excursion.”