Meanwhile, Guy Gibson’s 617 Squadron remained together and they were subsequently given the opportunity to deliver Barnes Wallis’s later weapons. The Cookie 5-ton bomb was carried by Lancaster bombers and used with great effect to attack submarine pens in France and German warship bases in the fjords of Norway. Although it proved a success, it was no more than a vast, conventional blast bomb. Barnes Wallis had in mind a very different secret weapon which would penetrate the ground and deliver such powerful shockwaves that it would bring down buildings and bunkers for a considerable distance around. Whereas a conventional bomb (no matter how large) did its damage through air-blast, Barnes Wallis’s revolutionary new bomb would generate a miniature earthquake, by setting up huge ground waves of energy. These could demolish a building from below.
Other solutions were sought to increase the penetrating power of high-explosive bombs. Towards the end of the war, a rocket-assisted high-impact bomb was conceived by the Royal Navy’s Captain Edward Terrell as an alternative answer. The rocket could give a smaller bomb the velocity needed to penetrate thick concrete. The weapon weighed only 4,500lb (2,000kg) and could be dropped from a safe altitude of 20,000ft (about 6,000m). When it had descended to 5,000ft (1,500m) a barometric fuse would fire a rocket motor in the tail. This accelerated the bomb to give it a final speed of 2,400ft/s (730m/s). This secret weapon was first carried under the wings of B-17 Flying Fortress bombers used by the 92nd Bomb Group on 10 February 1945 against the S-boat pens at IJmuiden, Netherlands. Altogether, 158 of these so-called Disney bombs were used operationally by the end of the war in Europe.
Barnes Wallis scaled down his proposals for his gravity-assisted penetrating bomb, and in 1944 designed instead the 12,000lb (5,400kg) Tallboy bomb, which could be carried by the current bombers. Later in the war, the Avro Lancaster improved to such an extent that it could just support a 10-ton payload and so, as we shall see, the 22,000lb (10,000kg) Grand Slam bomb was finally put into production. It was a secret weapon of unprecedented power. As in the case of the Tallboy bomb, the Grand Slam was spin-stabilized by its fins and was built with a thick, heavy steel case to allow it to penetrate deep layers of the ground unscathed. Dropped from high altitude, it would impact at nearly the speed of sound. During manufacture, hot liquid Torpex explosive was poured in to fill the casing and this took a month to cool down and solidify. Torpex (named because it had been developed as a TORpedo EXplosive) had more than 150 per cent the force of TNT. The finished bomb was so valuable that aircraft that could not drop their weapon in an abortive mission were ordered to return to base and land with the bomb intact, instead of jettisoning it over the open sea. Barnes Wallis had planned to create a 10-ton weapon in 1941, but it was not until June 1944 that the bomb was ready for use. It was first dropped on the Saumur rail tunnel from Lancaster bombers of 617 Squadron. No aircraft were lost on the raid, and one of the bombs bored 60ft (18m) through the rock into the tunnel, blocking it completely. These massive ‘earthquake’ bombs were also used on the great concrete stuctures that the Germans were building to protect their rocket storage bunkers and submarine pens, and caused considerable damage. The Valentin submarine pens at Bremen, Germany, were made with reinforced concrete roofs some 23ft (7m) thick yet they were penetrated by two Grand Slam bombs in March 1945.
These ground-penetrating bombs are among the secret weapons that have gone on to give rise to present-day developments. Remote guidance was added to the Tallboy bomb by the United States during the Korean War. The resulting weapon was the 12,000lb (5,400kg) Tarzon bomb, used with devastating effect against a deep underground control room near Kanggye. Bunker buster bombs were also dropped at the Ali Al Salem Air Base, Kuwait, in 1991 as part of Operation Desert Storm. At the outbreak of the First Gulf War none of the NATO forces possessed such a weapon, so some of the original Barnes Wallis bombs were brought out of museums and used as templates for the construction of 2-ton bombs. They were laser guided by the United States forces and proved highly effective.
During the late 1990s a nuclear bomb was being designed by the United States for use in tactical warfare. Known as the Robust Nuclear Earth Penetrator it underwent extensive design and development even though the use of nuclear weapons was prohibited by international agreement. Work on the project continued until it was finally cancelled by the Senate in 2005. Meanwhile, in 2007 the Boeing Company announced that they had carried out successful tests of their Massive Ordnance Penetrator (MOP) weapon at the White Sands Missile Range, New Mexico. This bomb, also known as the Big Blu and Direct Hard Target Strike Weapon, is a 30,000lb (14,000kg) penetration bomb designed to be delivered by a B-52 Stratofortress or a B-2 stealth bomber against heavily protected subterranean targets. This is a project for the United States Threat Reduction Agency, and is designed to hit the ground at supersonic speeds so that it can penetrate deeply prior to detonation. Most of the mass is in the casing, not the explosive component. All of his stems from the work of Barnes Wallis during World War II, so once again the legacy of these secret weapons remains with us to this day.
Carrying artillery and ammunition to the war front is a time-consuming and tedious business. Far better, the Germans realized, for the weapons to take themselves to the front. From the start of the war — and indeed in the Spanish Civil War, which was a prelude to World War II — the Germans began to look at ways of carrying explosives by plane, and dive-bombing soon became an early strategy in planning an attack. But the bombers were vulnerable, and losses were soon rising fast. So the Germans turned to designs for planes without pilots. These ideas could be far-reaching, because — since there was no crew whose lives could be put at risk — the planes themselves would be expendable. Nothing need be omitted in the search for an answer.
By 1942, Rheinmetall-Borsig AG had risen to the challenge, and announced the design for their Rheintochter (Rhine Maiden) surface-to-air missile. It was a remarkable device, a two-stage surface-to-air vehicle which was named from Wagner’s famed Ring cycle. The Rheintochter was designed with a cylindrical fuselage bearing four rounded steering fins operated by servo-mechanisms. Four large swept-back fins on the first stage kept the flight of this solid-fuel rocket-powered device stable in flight. A later modification substituted a liquid fuel engine, but even this did not provide the desired performance and — although many were launched — the project was never fully operational, and it was finally cancelled in December 1944.
In 1943 development was announced of the successor to the Rheintochter — it was the Rheinbote (Rhine Messenger) and was designed by the Rheinmetall-Borsig Company. This was a design for a slender 37ft (11.4m) rocket that could deliver a modest payload over distances up to 125 miles (200km). The solid propellant was to be diglycol dinitrate and the missile would be a four-stage rocket: the first stage would launch the main rocket from the ground before being discarded; the second and third stages would fire in succession, carrying the payload aloft, and the final fourth stage would fire it into its maximum altitude where it was set on its course to the target.
However, there was a major problem with accuracy. Each of the four stages was stabilized by four fins at the aft end of the rocket, and the stages were ignited in turn as the fuel charge from the previous stage reached the end of its burn. This was clearly a rocket of limited appeal, for it consumed 2 tons of steel in manufacture, with all the concomitant requirement for energy, it demanded more than half a ton of fuel propellant, yet it could deliver no more than a 44lb (20kg) explosive to its target. It produced no fragment damage and could make a crater no more than 5ft (1.5m) across. Other projects — like Herbert Alois Wagner’s design for the Schmetterling (Butterfly) — seemed to offer far more promise and informed opinion was that the rocket was militarily valueless. This cut no ice with the High Command; the weapon could be simply understood and a four-stage device was simply too good to miss. Hitler and General Hans Kammler (who reported to Reichsführer Heinrich Himmler directly) immediately ordered production of this worthless missile. Tests were carried out, but it proved impossible to calculate the accuracy because the impact craters were so small that they could not be found.