On September 8, 1943, the Second World War took a dramatic turn as Italian Marshal Pietro Badoglio, who had just replaced a deposed Benito Mussolini as Prime Minister, announced an armistice between Fascist Italy and the Allied Powers. The following day, a large Italian naval fleet, on its way to counter the Allied amphibious landings at Salerno, was ordered to break off and sail to Malta to prevent its ships falling into the hands of Italy’s former German allies. Commanded by Admiral Carlo Bergamini, the fleet included three battleships – including the flagship Roma – six cruisers, and eight destroyers. Not knowing the details of the Armistice, Bergamini was reluctant to surrender in Malta, and instead set course for La Maddalena naval base on the island of Sardinia. On approaching the base, Bergamini discovered it had been overrun by the Germans, and instead ordered the fleet to Bône – today Annaba – in French Algeria. But as the fleet passed through the Strait of Bonifacio separating Sicily and Corsica, it was suddenly attacked by a flight of German Dornier Do 217 medium bombers of Kampfgeschwader 100. The bombers had actually been trailing the fleet for some time, but Bergamini had assumed they were the air cover promised him by the Allies. But by the time the Italian anti-aircraft batteries opened fire, it was already too late. At around 3:50 in the afternoon bombs slammed into Roma and the battleship Italia, causing extensive damage. Her boiler rooms flooded and her engines out of action, Roma became a sitting duck. At 4:02, another bomb slammed into her starboard side, penetrating her ammunition magazines and touching off an enormous explosion. The ship quickly capsized and sank, taking 1,253 of her 1,849 crew – including Admiral Bergamini – with her.

This engagement was a significant moment in the history of warfare, for the weapons that sank the Roma were not ordinary bombs but sophisticated radio-controlled missiles known as Fritz X. Though precision-guided weapons or “smart bombs” might seem like a recent innovation, this technology – like so many others – was actually pioneered during the Second World War. And while these weapons arrived too late to affect the outcome of the conflict, they forever changed the way modern warfare is waged. This is the fascinating story of the birth of the Smart Bomb.

German research into guided munitions began in 1938 in response to Luftwaffe experiences in the Spanish Civil War. During that conflict, pilots of the Condor Legion – a volunteer air force sent to assist Nationalist leader Fransisco Franco – encountered great difficulty hitting moving targets such as ships at sea. Much of this early research was headed by engineer Max Kramer of the German Centre for Aerospace Research or DVL, who began fitting regular aircraft bombs with radio-actuated control surfaces. The weapon that would eventually sink the Roma was based on the Ruhrstahl PC 1400, a 1400 kilogram unguided armour-piercing bomb intended for use against heavily-armoured targets like battleships and cruisers. The name “Fritz X” was derived from the PC 1400’s original nickname, but the weapon was also variously known as the Ruhrstahl SD 1400, the Kramer X-1, the PC 1400X, or the FX 1400.

Kramer fitted the PC 1400 with a set of four forward stabilization fins and a guidance system built into an annular “box fin” assembly at the tail of the bomb. This system contained gyroscopes to keep the bomb stable in flight as well as a set of spoilers that could be deployed into the airstream to control the bomb in roll, pitch, and yaw. These spoilers were controlled via a Strasbourg radio receiver whose receiver antennas were housed in aerodynamic plastic fairings mounted around the perimeter of the box fins. Aboard the attacking aircraft, the bombardier used a Kehl radio transmitter and joystick to guide the weapon visually to the target, a set of bright red flares in the bomb’s tail increasing its visibility. However, the primitive radio guidance system only allowed the spoilers to be set to “full up” or “full down”, requiring great skill on the part of the bombardier. The transmitter could be set to 18 different frequencies between 27 and 60 Megahertz, allowing multiple aircraft to drop bombs at once without their guidance signals interfering with each other.

The Fritz X became fully operational in the spring of 1943, with 750 being produced and deployed.

The weapon was only deployed by one squadron – Gruppe III of KG-100 Wiking – whose Dornier Do 217K-2 medium bombers were fitted with special bomb racks for the Fritz X and Kehl radio transmitter sets. Due to the glide angle of the bomb, attacks were typically made from an altitude of 5,500 metres and a minimum range of 5 kilometres, with the launching aircraft immediately decelerating after release so the bombardier could keep the bomb in his sights. From standard launch altitude and range, a skilled bombardier could theoretically make a maximum correction of 500 metres in the bomb’s range and 350 metres in its bearing and place 90% of bombs within a 30 metre radius of the aiming point. Those bombs that did hit were capable of penetrating 5 metres of armour – more than enough to sink a battleship.

The Fritz X made its combat debut on July 21, 1943 during a raid on Augusta harbour in Sicily. Several other attacks followed around the island, but no hits were recorded. The weapon’s first successful use was in August, when KG 100 sank a Royal Navy corvette and damaged another in the Bay of Biscay. On September 9, the unit carried out its historic attack against the defecting Italian fleet off Sicily, sinking the battleship Roma and badly damaging the Italia. Two days later, they attacked the Allied landing fleet off Salerno, barely missing the light cruiser USS Philadelphia but scoring a direct hit on her sister ship USS Savannah. The bomb penetrated the roof of C turret and detonated in the lower ammunition-handling room, severely damaging her hull, blowing out her boiler fire and killing 197 crewmen. Savannah languished, half sunken, for nearly six hours before her boilers were relit and the ship limped to Malta for repairs. On September 13th and 16th similar fates befell the Royal Navy light cruiser HMS Uganda and the battleship HMS Warspite when Fritz X bombs sliced through seven decks and exploded near the ships’ keels. Both ships were severely damaged and had to put into Malta for extensive repairs. Other ships damaged by Fritz X attacks off Salerno include the Dutch sloop HNLMS Flores, the British destroyer HMS Loyal, and the American merchantmen SS James W. Marshall and SS Bushrod Washington – though the latter two may actually have been hit by conventional bombs.

In early 1944, KG 100 was deployed against the Allied landing fleet off Anzio. By this time, however, the deficiencies of the Fritz X were starting to become apparent. The line-of-sight guidance system meant the launching aircraft had to maintain a straight, steady course over the target, making them highly vulnerable to fighter attack. The Fritz X also could not be deployed in anything but the lightest cloud cover, and was far less accurate in combat than in training; indeed, throughout the weapon’s deployment, only 30% of launches resulted in hits, while only one ship – the Roma – was ever sunk. Even worse, by the time of the Anzio landing, the Allies had figured out how to jam the Fritz X’s radio control system. At first, jamming had proved surprisingly difficult, since the Strasbourg receiver could be tuned to a variety of frequencies and was designed to ignore transmissions coming from ahead of – rather than behind – the bomb. However, British radio engineers soon discovered that by targeting the receiver’s intermediate frequency, the system could be effectively jammed no matter what frequency the Germans selected. The Type 650 jamming transmitter was first deployed aboard Allied ships at Anzio in early 1944 and succeeded in preventing the Germans from scoring any direct hits with the Fritz X. By the time of the Operation Overlord landings in Normandy in June 1944, radio jamming plus overwhelming Allied air superiority had rendered the Fritz X all but useless, and it was soon withdrawn from service.

However, the Fritz X was not the only guided air-to-ground weapon deployed by the Germans during the war. In 1939, the Gustav Schwartz Propeller Works designed a glide bomb to allow bombers to attack a target from beyond the range of anti-aircraft batteries. The bomb did not have an active guidance system, and instead was fitted with an autopilot to maintain a straight course to the target. In 1940, however, a team of engineers at aircraft manufacturer Henschel led by Dr. Herbert Wagner converted the Schwartz design into a powered, guided missile by fitting it with a rocket motor and the same Kehl-Strasbourg radio command system as the Fritz X. Known as the Henschel Hs 293, the weapon carried 550 kilograms of explosives but, unlike the Fritz X, had no armour-piercing capability and was designed for use against unarmored merchant and auxiliary vessels. To this end, the nose of the missile was fitted with a donut-shaped kopfring that, on impacting the water, ensured that the Hs 293 struck the target’s hull perpendicularly like a torpedo. The weapon was steered through the use of elevators and ailerons operated by electric solenoids and jackscrews; no rudder was fitted.

Thanks to its rocket propulsion, the Hs 293 could be used at greater ranges and lower altitudes than the Fritz X. Upon release, the Walter HWK 109-507 rocket engine slung beneath the fuselage ignited, delivering 5.9 kilonewtons of thrust for 10 seconds and accelerating the missile to a maximum speed of 960 kilometres per hour. This engine was powered by a highly concentrated hydrogen peroxide monopropellant decomposed into high-temperature steam by a sodium permanganate catalyst, and was originally developed as a Rocket Assisted Takeoff or RATO pod to help lift heavily-loaded transport aircraft into the air. Once the engine had burned out, the attack procedure was the same as with the Fritz X, the bombardier using red flares in the missile’s tail to guide it towards its target.

Development of the Hs 293 began in early1940 at the Luftwaffe research centre at Peenemünde on the Baltic – where many other advanced German weapons like the V1 flying bomb and V2 ballistic missile were also developed. The first unpowered drops took place between May and September, while the first powered flight was conducted on December 18. The weapon proved stunningly accurate, scoring a direct hit on the test target – a small barn – on only its second live firing. A derelict 5,000 ton ship just off the coast was used for testing, and was soon nearly obliterated by dozens of direct hits. Operators were first trained on a ground-based simulator, then allowed to make three live launches; most trainees scored direct hits on their third launch. The Hs 293 was first used in combat by KG 100 on August 25, 1943, successfully striking the British sloop HMS Bideford in the Bay of Biscay – though the warhead failed to detonate. Two days later, however, the squadron succeeded in sinking the sloop HMS Egret. Over the following year, Hs 293s damaged or sunk some 30 Allied ships, while in August 1944 they were used – unsuccessfully – to attack bridges over the Sée and Sélune rivers in Normandy – the first use of an air-launched standoff missile in military history. However, like the Fritz X before it, the Hs 293 was eventually rendered ineffective by Allied radio jamming and air superiority and was largely withdrawn from service in late 1944. The last recorded use of the Hs 293 was in April 1945, when a special unit of KG 200 attempted to destroy bridges across the Oder river to slow down the advancing Soviets. The attack was a failure, with no hits recorded.

Undeterred, the Germans investigated several ingenious methods for getting around the jamming problem, including converting the Hs 293 to wire guidance. The radio equipment was removed and a pair of streamlined pods added to the wingtips containing 18 kilometres of fine, 0.2mm piano wire. Similar spools aboard the launching aircraft carried a further 12 kilometres for a maximum range of 30 kilometres. Command signals from the bombardier travelled through the wires as they unspooled behind the missile, rendering it immune to radio jamming. Even more impressive was the Hs 293D, which featured television guidance. The Fernes Company, in collaboration with the German Post Office, succeeded in creating a miniature 224-line television camera and transmitter package called “Tonne A”, which measured 17x17x40 centimetres and weighed only 130 kilograms – making it ideal for mounting in the nose of a missile. While still vulnerable to radio jamming, this system allowed the attacking aircraft to take evasive action after launching the missile, as the bombardier no longer needed a clear view of both missile and target. However, the war ended before either weapon could see combat.

One final German “smart bomb” of note was the Blohm und Voss Bv-246 Hagelkorn or “Hailstone”, an unpowered glide bomb designed to attack the LORAN radio beacons used by Allied bombers for navigation. Designed to use as few strategic materials as possible, the Bv-246 had wings made of magnesite cement moulded around a steel spar and carried 435 kilograms of explosives. Carried aloft by a fighter aircraft like the Focke-Wulf Fw 190, the bomb was to be released up to 200 kilometres from the target, whereupon it would automatically home in on and destroy LORAN transmitters using a passive seeker device called Radieschen. Testing began in late 1944 at the Unterlüss Proving Ground in lower Saxony, but unfortunately the guidance system proved troublesome and only 20% of the test vehicles flew properly. However, when the V-1 flying bomb campaign against Britain proved more successful than anticipated, the Bv-246 was cancelled without ever seeing service. Nonetheless, it pointed the way toward modern anti-radiation missiles like the American AGM-45 Shrike and AGM-88 HARM.

But while the Germans were the first to deploy guided weapons in combat, the Allies were not far behind, and by the end of the war actually succeeded in surpassing German technology. In the now largely forgotten China-Burma-India theatre of operations, much effort was expended in disrupting Japanese supply lines by destroying bridges along the Burma Railway. However, these narrow wooden bridges proved challenging for airmen to hit, and much ordinance was wasted in unsuccessful attacks. In response, Major Henry Rand and Thomas O’Donnell invented the Vertical Bomb 1 or VB-1. This consisted of a conventional 1,000 pound general purpose AN-M65 “iron bomb” fitted with a special box-fin tail unit. This contained gyroscopes to stabilize the bomb in roll, a flare to increase its visibility, and a set of ailerons controlled by the bombardier using a BC-1156 transmitter and joystick in the launching aircraft. Unlike the Fritz X and other German guided weapons, the VB-1 had no pitch or range control and only be adjusted in azimuth – hence its eventual designation of AZimuth ONly or AZON. This meant that the bombardier still had to release the bomb accurately to ensure it did not fall short or long of the target, making it best-suited to attacking long, narrow targets like bridges.

The AZON was first deployed in November 1944 by Consolidated B-24 Liberator bombers the 493rd Bomb Squadron based an Pandaveswar Airfield in India. Over the next nine months, the 493rd succeeded in destroying 41 bridges in Burma and Thailand – including the famous Bridge on the River Kwai – using 1,357 bombs, achieving a hit rate of around 12%. Perhaps the greatest testament to the AZON’s effectiveness came on December 28, 1944 when the 493rd used just 9 AZONs to demolish the rail bridge at Pyinmana, Burma, which had withstood bombardment by thousand of conventional munitions over the previous two months.

The AZON was also used in the European Theatre by the 458th Bombardment Group based at RAF Horsham St Faith in England. Between June 8 and September 13, 1944, the 458th carried out 9 AZON missions against railway bridges and oil refineries in France, the Netherlands, and Germany – though with considerably less success. Unlike in Burma, bombers over Europe had to contend with intense antiaircraft fire and fighter attacks, which often forced them to break off from their steady courses and interrupt the bombardier’s view of the target and weapon. A more advanced version of the AZON called VB-4 or RAZON – Range and AZimuth Only – which used a 2,000-pound bomb and allowed for pitch control – was in development since 1942, but entered service too late to see combat. After the war, an even more powerful 12,000-pound version called the VB-13 or ASM-A-1 Tarzon – effectively a British Tallboy “bunker buster” bomb fitted with a radio controlled tail unit – was developed and briefly used in the Korean War before being retired in 1951 – and for more on these enormous weapons, please check out our previous video That Time Disney Helped Give the World a Weapon of Mass Destruction. But while the AZON played a relatively minor role in the Second World War, it pioneered a technique still used today in weapons like the Joint Direct Attack Munition and Paveway, in which regular “dumb bombs” are converted into precision guidance munition by fitting them with a standardized tail unit or seeker head.

Another Allied guided weapon tested during the war was the Aeronca Glide Bomb or GB-1, which was originally intended to achieve not greater accuracy but rather greater range. Little more than a standard 1,000 or 2,000 pound bomb fitted with 12-foot wooden wings, a twin-boom tail unit, and a simple autopilot, the GB-1 was designed to be released up to 32 kilometres from the target, allowing the attacking aircraft to avoid anti-aircraft defences. The weapon had the further advantage of being more likely to hit the sides of buildings and other structures, rather than just exploding harmlessly in the open like conventional vertically-dropped bombs.

Too large to fit in an aircraft’s bomb bay, the GB-1 was instead carried in pairs under the wings of a Boeing B-17 bomber. After the completion of initial testing, the first weapons were sent to England in September 1943 for use by the 41st combat bomb wing of the 8th Air Force. However, local commanders saw fighter aircraft as a greater threat than anti-aircraft guns and deemed the GB-1 too inaccurate, so the weapon was shelved. By early 1944, however, the Luftwaffe’s strength had become so depleted that it was decided to finally give the GB-1 a try. On May 28, 1944, the 41st attacked the Eifeltor Marshalling Yard at Cologne, with 54 B-17s releasing 108 GB-1s. Yet despite ideal conditions with little wind and good visibility, most of the weapons drifted far off target and only a handful actually struck the marshalling yard. Thus, while the bombers successfully avoided anti-aircraft fire and all returned safely to England, the GB-1 was deemed a failure. Nonetheless, more than 1000 more would be dropped over Germany before the end of the war.

However, more advanced versions of the GB-1 were soon developed in order to remedy these shortcomings. The GB-4, like the Henschel Hs 293D, incorporated a small television camera in its nose that allowed it to be guided towards its target irrespective of the launching aircraft’s speed or course. The weapon was first deployed in July 1944, but combat trials revealed that the television image was too fuzzy to be usable on any but the clearest days. Though around 1,000 were produced, only a few were ever launched before the project was abandoned. The US Army Air Force also experimented with a powered variant called the JB-4 propelled by a pulse-jet engine similar to that used on the German V-1 flying bomb; however, this weapon was not yet ready by the end of the war and was cancelled soon afterward.

Even more sophisticated was the GB-5, which used a television-based light-contrast seeker to home in on targets – like ships at sea – that were considerably darker or lighter than their surroundings; the GB-6, which had an infrared homing system; and the GB-7, which could either home in on enemy radar transmissions or ride a radar guidance beam projected by the launching aircraft. However, none of these variants were ready either by war’s end.

One variant of the GB-8 that did see limited use was the GB-8, which, like the Henschel Hs 293, used a radio command link and coloured flares to allow the bombardier to guide the weapon towards the target. The GB-8 was first used in early 1945 against the German E-boat pens at Le Havre and La Pallice in France, and while the weapon was nominally more accurate than conventional bomb, it suffered from the same drawbacks as the Fritz X and Hs 293 – namely, that the launching aircraft had to fly a slow, steady course over the target, making them vulnerable to anti-aircraft fire and fighter attack.

The U.S. Navy also experimented with guided munitions. Inspired by the early successes of the German Fritz X and Henschel Hs 293, in late 1943 the Navy issued a requirement for an unpowered anti-ship glide bomb, the contract for which was awarded to McDonnell Aircraft in the summer if 1944. Dubbed the LBD-1 Gargoyle, McDonnell’s weapon resembled a small unpowered aircraft 2.5 metre wingspan, a v-tail, 3-metre fuselage containing a 1,000-lb armour-piercing bomb. The Gargoyle was designed for use by carrier-based aircraft and could be released up to 8 kilometres from the target, whereupon the bombardier would guide the weapon using radio command and flares in the tail. Just before impact, an Aerojet solid-rocket motor in the rail was ignited, providing 4.4 kilonewtons of thrust for 8 seconds and accelerating the weapon to 970 kilometres per hour. Despite the Gargoyle’s initial promise, however, the development program was plagued by technical difficulties, such that the first test flight did not take place until July 1946 – nearly a year after the end of the war. Trials dragged on for another four years until, in December 1950, the Gargoyle project was finally cancelled.

Far more successful than the Gargoyle was the Bat, which arguably holds the title of the most sophisticated guided missile ever deployed during the Second World War. The Bat originated in 1941 as an RCA project to build a television-guided anti-ship missile similar to the Hs 293D. In June 1942 the design was modified to use semi-active radar guidance, wherein the missile homed in on reflections from a radar beam projected by the attacking aircraft. Originally known as the Pelican, the weapon was designed by the National Bureau of Standards in collaboration with the Navy Bureau of Ordnance, MIT, Bell Telephone Laboratories, and Bendix Aviation. It was unpowered, had a length of 3.6 metres, a wingspan of 3 metres, weighed 270 kg, and was armed the same 1,000 pound general purpose bomb as the AZON. Power for the controls was provided by small wind-driven generator.

Drop tests of the Pelican began in December 1942 at Naval Air Station New York, but while the weapon proved moderately successful – hitting its target in about half of launches – the range of the radar guidance beam was found to be too short, putting the launching aircraft at risk of being spotted and fired upon. Thus, in 1944, the Pelican was cancelled in favour of a more sophisticated version using active radar guidance, which was designated the Special Weapons Ordnance Device or SWOD Mk.9 Bat. Unlike the other weapons covered in this video, the Bat was a truly autonomous “fire and forget” weapon, requiring no outside guidance commands after launch. Instead, it used an active radar system in a nose-mounted dome to home in on its target.

The Bat began developmental testing in the summer of 1944 at the Naval Ordnance Test Station at Chincoteague Island, Virginia, and was declared combat-ready in January 1945. Though many aircraft were modified to launch the Bat, including the Vought F4U Corsair fighter and Grumman TBF Avenger torpedo bomber, the weapon was mainly deployed aboard Consolidated PB4Y Privateer naval patrol aircraft. The Bat was first used in combat in April 1945 off Borneo, successfully damaging or sinking several Japanese ships including the coastal defence vessel Aguni. Like the AZON, the Bat was also used to attack bridges along the Burma Railway, though in this role it was considerably less successful as its relatively primitive radar guidance system was easily confused by ground clutter and other interference. Indeed, when used against ships close to shore, the Bat tended to veer off target and home in on other large objects like docks, hills, and mountains. Consequently, though 2,600 Bats were produced and deployed, relatively few were actually launched before war’s end. Nonetheless, it was the first fully-autonomous self-guided weapon to be deployed in combat, and set the template for guided weaponry for decades to come. Today, precision-guided bombs and missiles, steered by radio, radar, laser beams, or even GPS, can hit targets just a few metres across from altitudes of thousands of metres and ranges of hundreds of kilometres – a far cry from the indiscriminate area bombing tactics of the Second World War.

Before ending this video, it is worth mentioning one of the strangest chapters in the history of guided weapons: Project Pigeon. In 1942, behaviourist B.F. Skinner – most famous for developing the principle of operant conditioning – began studying the feasibility of guiding a missile using – you guessed it, pigeons. Skinner’s concept involved training pigeons to recognize and peck at images of enemy ships. They would then be placed in a special compartment in the nose of a missile with an electrically-conductive screen on which was projected images from a television camera. A guidance system would sense the pigeon’s pecks and use them to adjust the missile’ trajectory and keep the target image in the centre of the screen, guiding the missile all the way to impact. Incredibly, ground-based simulations proved that the system was workable, and Skinner tried to convince the Navy to try it out in a Pelican missile. However, Naval officials dismissed the whole concept as impractical and outlandish, and Project Pigeon was never deployed in combat.