with the 40 millimeter guns. The target, however, was able to move closer inshore and escaped in the fog which closed around her like a shroud. The submarine lurked on the surface off Hokkaidō on 31 July and again tangled with some of the numerous Japanese patrol craft. She sighted a patrol boat at and closing. Thornback’s five-inch (127 mm) deck gun was trained out, but her crew could not keep their sights on the attacker through the telescopes and switched to open sights. Meanwhile, the 40 millimeter gun opened a devastating barrage at the enemy craft as it came steadily on a collision course. These shells continually hit the escort ship along the waterline and in the pilot house, probably killing the occupants on the bridge. Thornback had passed her target once at and came about for a second pass when the forward torpedo room reported sharp noises forward. Further amplification showed that the noise was caused by enemy machine gun bullets striking the submarine's hull. Resuming the attack, Thornback swung back into action, with visibility only and lessening. Her 40 millimeter fire continued to maul the Japanese vessel, shooting away one of her masts and leaving her limping shoreward at only . After securing from battle stations, Thornback passed through an oil slick and noted a mast from the heavily hit patrol craft. Later on 31 July, Thornback rendezvoused with Sea Poacher off Kesennuma and proceeded north to pick up submarine en route to a projected shore bombardment mission against Hokkaidō. The sight of the three submarines cruising on the surface moved Thornback’s commander to write: "On this clear and sunny day, the three ships in perfect column on a flat sea made a beautiful picture tearing along at 18 knots." At 14:02 on 1 August, this part of "Abe's Abolishers"—Thornback, Angler, and Sea Poacher—made landfall off their target of Urakawa, Hokkaidō. They swung parallel to the beach with guns manned and ready. Twelve minutes later, slowing to 10 knots (19 km/h), Thornback and her consorts opened fire with and 40 millimeter batteries at a range of . The first few rounds from Thornback’s five-incher went wild, but the crew soon locked onto the range. Firing by hand after the foot firing plunger broke off, Thornback’s gunners eventually sent 100 rounds of five-inch (127 mm) shells shoreward, heavily damaging a factory and a power plant. "The firing took