There were three main reasons why Barnes Wallis' 'earthquake bomb' designs (both the 12,000 lb Tallboy and 22,000 lb Grand Slam) weren't used against Japanese targets on Okinawa. The first, and simplest, was that these weapons were designed for use on the British Avro Lancaster bomber. This aircraft had a long, shallow bomb bay, capable of fitting in these long, slim weapons with only minor changes. The equivalent American aircraft, the B-17 and B-29, had short, deep bomb bays. As such, these aircraft could not carry either Tallboy or Grand Slam without serious modifications. The invasion of Okinawa, and indeed much of the fighting in the Pacific Theatre, was a primarily American affair. The only British forces involved were the carriers of the British Pacific Fleet. Lancasters were not deployed to the Pacific during WWII - planning was underway for a force of British and Commonwealth heavy bombers, called Tiger Force, to be deployed as part of the bombing campaign against Japan, but this was not carried out before the end of the war. Tiger Force would, however, have included No 9 and No 617 Squadrons RAF, which were equipped with aircraft capable of carrying both bombs.

The second reason is that these weapons were only really capable of being used against easily identifiable targets. They had to be dropped from high altitudes, to build up enough speed to penetrate the earth and create the desired effect. Bombing from high altitude meant that it was very easy to miss. To do this with accuracy, the British developed a special bombsight, the Stabilized Automatic Bomb Sight (SABS). The SABS was a complex system, requiring multiple inputs, including air temperature, wind speed and direction, and the parameters of the bomb. This was required because the destructive effect of the bombs was limited on a miss on a hardened target. Trying to bomb a target that could be observed and identified was difficult enough. Doing it on a camouflaged target was much more difficult.

The final reason was that these bombs were very difficult to produce. Many of the parts that went into them were hand-made, while the casings themselves were a single, massive casting. This had to be machined down to a precise, very fine shape. Even filling them with explosives was difficult, due to the sheer mass. The Torpex filling of a Grand Slam could take up to a month to cool. This meant that the bombs were rare, and could only be used on the most important targets. Crews of aircraft carrying them were instructed that, should they have to turn back to base before dropping their bombs, they were not to jettison them as was typical. The RAF was more willing to lose a crew than it was to lose one of these bombs. The defences on Okinawa could be destroyed through other methods. As such, they would have been considered to be not worth targeting with either Tallboy or Grand Slam.