As late April turned to May, the Shuri continued to stand against a massive bombardment from land air and sea. By March 30th, the average rate of advance was just 50 yards per day. For many officers and senior NCOs, the fighting brought back unpleasent memories of the Western front, though most who saw both considered Okinawa worse. That the island was to be a bloodbath was not lost on General Eichelburger during the planning for Operation Buckshot, and so he'd been granted permission to call in help.
The RAFs no. 617 squadron, more commonly known as "The dambusters" had gained fame for their destruction of several key dams in Germany in 1943, and crippling the battleship Tirpitz in the Autumn of 1944. They'd begun transferring to the Pacific back in December, intending to help in the battle of Formosa. However delays in getting aircraft and ordinance ready meant they weren't operational until April. The higher ups in the Pacifoc had been clncered about the effect that more foreign assistance would have on morale, but in fact the soldiers were overjoyed that they were getting help to drive the Japanese out of their tunnels.
The dambusters had arrived with dozens of six ton "tallboy" and several 11 ton "grand slam" earthquake bombs, and were provided with American copies to replace them. The attacks initally encountered problems however. The accuracy was actually considered superb by their American counterparts, as the heavy bombs punched straight through the jet stream. The issue was the actually finding a target to hit was not easy. Many initial targets were simply exit points for the Japanese ambushes, which were rarely near any major troop areas. One radioman likened it to "Trying to kill an ant colony by throwing a cherry bomb at the hill." In many cases all these bombs did was make the exit points larger, and didn't kill many enemy soldiers at all.
Later, the marines operating underground tried to pinpoint enemy barracks and other large chambers underground, but even when they did, translating their location so that a bomber crew five miles up would know where to aim was difficult. Accuracy improved over time, but the dambusters never reached the level of fame they achieved in Europe.
Meanwhile the infantry tried their own methods for flushing out the Japanese. In some cases seabees brought in drilling equipment to bore holes into the tunnels and caves, into which water, napalm, gasoline, or even field latrine sewage were poured in. The Japanese did have pumps, but as fuel ran out many of the lower areas became uninhabitable. Disease became rampant as the sweltering tunnels filled with water and bodies, and at its peak nearly 20,000 American soldiers were listed sick, and 3,000 would ultimately die of diease.
Conditions for the Japanese were no less brutal. Many wounded were forced to remain at the front, as the underground hospitals soon ran out of room and medicine. In one rare case of the dambusters success, the headquarters of the 44th mixed brigade was cut off when a grand slam caved in the only exit. 1,500 soldiers were trapped, including two generals and 120 Okinawan schoolgirls who'd been conscripted as staff and medical personel. The HQ had a ventilation shaft that didn't require power, but it was too small to exit.
The tunnel soon became known to the Americans, but even after the end of the fighting there were concerns that the Japanese would not surrender. As such, the HQ (Called "the den" by marines) was not opened until June of 1946, by which point only 46 men remained alive, having subsisted off of leaking rainwater, and their comrades bodies. Even after the fighting ended, the den became one final horrific bookend to the terrors of Kuribayashi-style warfare.