Fritz X was a German guided anti-ship glide bomb used during World War II. Developed alongside the Henschel Hs 293, Fritz X was one of the first precision guided weapons deployed in combat. Fritz X was a nickname used both by Allied and Luftwaffe personnel. Alternative names include Ruhrstahl SD 1400 X, Kramer X-1, PC 1400X or FX 1400 (the latter, along with the unguided PC 1400 Fritz nickname, is the origin for the name "Fritz X").
History
Fritz X was a further development of the PC 1400 (Panzersprengbombe, Cylindrisch 1,400 kg)German Wikipedia's WW II PC-series bomb specifications, German for "armour-piercing bomb, cylindrical". armour-piercing high-explosive bomb, itself bearing the nickname Fritz. It was a penetration weapon intended to be used against armoured targets such as heavy cruisers and battleships. It was given a more aerodynamic nose, four stub wings, and a box-shaped tail unit consisting of a roughly 12-sided annular set of fixed surfaces and a cruciform tail with thick surfaces within the annulus, which contained the Fritz Xs aerodynamic controls.
The Luftwaffe recognised the difficulty of hitting moving ships during the Spanish Civil War.Fitzsimons, Bernard, ed. "Fritz-X", in The Illustrated Encyclopedia of 20th Century Weapons and Warfare (London: Phoebus, 1978), Volume 10, p. 1037. German engineer Max Kramer, who worked at the Deutsche Versuchsanstalt für Luftfahrt (DVL), had been experimenting since 1938 with remote-controlled free-falling bombs and in 1939 fitted radio-controlled spoilers.Fitzsimons, "Fritz-X", p. 1037. In 1940, was invited to join the development, since they already had experience in the development and production of unguided bombs.Christopher, John. The Race for Hitler's X-Planes (The Mill, Gloucestershire: History Press, 2013), p. 134.
Fritz X was guided by a Kehl-Straßburg radio control link, which sent signals to the movable spoilers in the thick vertical and horizontal tail fin surfaces, within the annular tail fin structure. This control system was also used for the unarmoured, rocket-boosted Henschel Hs 293 anti-ship ordnance, first deployed on 25 August 1943. The Straßburg receiver antenna installations on the Fritz X were aerodynamically integrated into the trailing edge of the annular surfaces of the tail fin, non-metallically encapsulated within four "bulged" sections in the trailing edge. This design feature of the FuG 230 Straßburg receiver installation is like the Azon (US contemporary guided bomb), which had its receiving antennas placed in the four diagonal struts bracing the fixed sections of its tail fins.
Minimum launch height was – although was preferred – and a range of was necessary.Christopher, p.134. As it was an MCLOS-guidance ordnance design, the operator had to keep the bomb in sight at all times (a tail flare was provided, as with the Azon, to assist the operator in tracking the weapon) and the control aircraft had to hold course, which made evading gunfire or fighters impossible. Approximately 1,400 examples, including trial models, were produced.
Control setup
The Fritz X possessed a spoiler-based control setup on its tail fin unit, using three sets of aerodynamic control spoiler systems, with two of them giving control in the pitch and yaw axes, differentially operating and constantly oscillating rapidly under direct control from the Kehl-Straßburg radio control link. The roll control setup, operating autonomously and not under control from the deploying aircraft, oscillated similarly to those under the externally controlled sets, and were on the outboard sections of the horizontal tailfin surfaces within the annular set of outer tailfin surfaces. These were like the American Azon ordnance's aileron control surfaces in their purpose, commanded by an internal gyroscope in the tail's central housing in both the Azon and Fritz X, to keep the ordnance level during its trajectory. The inboard set of spoiler surfaces in the tailfin's horizontal surfaces, which used a set of wing fence-like flat surfaces for airflow separation from the autonomous roll control spoilers, controlled the pitch angle after release and were controlled by the radio control link, giving the Fritz X's bombardier in the deploying aircraft the ability to control the range of the drop, a capability that the Azon did not have. The yaw control spoilers housed in the vertical tail fin surfaces were also under control through the radio link, and had similar "fence" surfaces to guide airflow over them. All three spoiler surface sets barely protruded from the surface during operation, with the pair of spoiler systems under external control having a degree of "proportionality" in their operation by varying the "dwell time" spent on one side or the other during their rapid rate of oscillation from side to side when a control input was sent to them.
Combat procedure
The Fritz X was steered by the bombardier in the launching aircraft over a radio link between the aircraft's Kehl transmitter and the weapon's Straßburg receiver. The bombardier had to be able to see the target at all times, and like the Azon, the Fritz X had a flare in the tail so it could be seen from the controlling aircraft for its MCLOS-form guidance to control it properly. The disadvantage with this — in comparison to fully autonomous-guidance glide bombs like the operational U.S. Navy's Bat radar-homing glide bomb, used against Japan in 1944–45 — were that the aircraft had to be flown towards the target on a steady course and that as the missile neared its target it became possible to misguide it by jamming its radio channel.
Unlike the Hs 293, which was deployed against merchant ships and light escort warships, the Fritz X was intended to be used against armoured ships such as heavy cruisers and battleships. The Fritz X had to be released at least from the target. The plane had to decelerate immediately after bomb release so the bombardier could see the bomb and guide it; this deceleration was achieved by making a steep climb and then levelling out. The bombardier could make a maximum correction of in range and in bearing. The bomber was vulnerable to fighter attack and ship-based air defence weapons while maintaining a slow, steady course so the bombardier could maintain visual contact to guide the bomb.Bogart, Charles H. "German Remotely Piloted Bombs" United States Naval Institute Proceedings November 1976 pp.62–68 When working properly, the missile was able to pierce 130 mm (5.1 in) of armor.
Accuracy is the main reason for developing a weapon system of this kind, rather than continuing to use unguided bombs. A skilled bombardier could guide 50% of the bombs to within a 15 m (50 ft) radius of the aiming point, and about 90% hit within a 30 m (100 ft) radius (some sources say 60% hit within 4.6 metre radius).
Usage in combat
The only Luftwaffe unit to deploy the Fritz X was Gruppe III of Kampfgeschwader 100 Wiking (Viking), designated III./KG 100; the bomber wing itself evolved as the larger-sized descendant of the earlier Kampfgruppe 100 unit in mid-December 1941. This unit employed the medium range Dornier Do 217K-2 bomber on almost all of its attack missions; in a few cases near the end of its deployment history, Dornier Do 217K-3 and M-11 variants were also used. The Fritz X had been initially tested with a Heinkel He 111 bomber, but was never taken into combat by this aircraft. A few special variants of the troublesome Heinkel He 177A Greif long-range bomber were equipped with the Kehl transmitter and proper bombracks to carry the Fritz X, and it is thought that this combination might have seen limited combat service, at least with the combinations known to have been involved in test drops. It was found that the launch aircraft had to "toss" the bomb slightly, climbing and then descending, to keep it in view ahead.
The Fritz X was first deployed on 21 July 1943 in a raid on Augusta harbour in Sicily. Several attacks around Sicily and Messina followed, but no confirmed hits were made and it appears the Allies were unaware that the large bombs being dropped were radio-guided weapons.RL 10/493: Tätigkeitsbericht über Einsatzperiode das K.G. 100 mit F.K. in der Zeit von 12.7.43 – 30.4.44. [Activity Report of Missions of KG 100 with Guided Weapons in the Period from 12.07.43 to 30.04.44.]
On 9 September, the Luftwaffe achieved their greatest success with the weapon. After Pietro Badoglio publicly announced the Italian armistice with the Allies on 8 September 1943, the Italian fleet had left La Spezia and headed to Tunisia. To prevent the ships from falling into Allied hands, six Do 217K-2s from III. Gruppe of KG 100 (III/KG 100) took off, each carrying a single Fritz X. The Italian battleship , flagship of the Italian fleet, received two hits and one near miss, and sank after her magazines exploded. 1,393 men, including Admiral Carlo Bergamini, died. Her sister ship, Italia, was also seriously damaged but reached Tunisia.
The American light cruiser was hit by Fritz Xs at 10:00 AM on 11 September 1943 during the invasion of Salerno, and was forced to retire to the United States for eight months of repairs. A single Fritz X passed through the roof of "C" turret and killed the turret crew and a damage control party when it exploded in the lower ammunition-handling room. The blast tore a large hole in the ship's bottom, opened a seam in her side, and blew out all fires in her boiler rooms. Savannah lay dead in the water with her forecastle nearly awash, and eight hours elapsed before her boilers were relit, allowing the ship to get under way for Malta. USS Savannah lost 197 crewmen in this attack. Fifteen other sailors were seriously wounded, and four more were trapped in a watertight compartment for 60 hours. These four sailors were rescued when Savannah had arrived at Grand Harbor, Valletta, Malta on 12 September.
Savannahs sister ship, , had been targeted earlier the same morning. The Fritz X just missed the ship, exploding about 15 metres away. Damage was minimal.See Barbara Tomblin's With Utmost Spirit: Allied Naval Operations in the Mediterranean, 1942–45 (Lexington: The University Press of Kentucky, 2004), 273. Tomblin cites as her source the original action reports filed by Philadelphia which clearly indicate the bomb missed. The erroneous notion that Philadelphia was hit emerged from an article in Proceedings in 1976 by Charles Bogart, and was subsequently repeated.
The Royal Navy's light cruiser was hit by a Fritz X off Salerno at 14:40 on 13 September. The Fritz X passed through seven decks and straight through her keel, exploding underwater just under the keel. The concussive shock of the Fritz X's underwater detonation close to Ugandas hull extinguished all her boiler fires, and resulted in sixteen men being killed, with Uganda taking on 1,300 tons of water. Uganda was towed to Malta for repairs.