Henschel Hs 129

The Henschel Hs 129 was the only aircraft of World War II - and, apart from today's A-10, virtually the only aircraft in all history - to be designed explicitly for destroying hostile amour. Apart from the Soviet Sturmovik, which was a more versatile armoured attacker, the Allies had no aircraft in this class. All the RAF had were a few Hurricanes fitted with 40-mm guns; which by comparison were totally inadequate. Yet Hitler's Germany completely failed to foresee how crucially important the Hs 129 would become, and there were nothing like sufficient numbers to make much impact on the tide of Soviet armour in 1944-45.

When the infant Luftwaffe was laying its plans for the future in 1935, it was generally believed that aircraft could do little to influence a land battle. If they were heavily armoured, they would be slow and sluggish, and their weapon load would be severely restricted. The effect of a few bullets or bombs seemed likely to be minimal, but in the Spanish Civil War of 1936-39 aircraft were seen to be not only effective but sometimes decisive (although against troops in unprepared positions). In April 1937 the Technische Amt issued a specification for a close support aircraft, to carry at least two 20-mm cannon and to have two low-powered engines and the smallest possible size, with armour and 75-mm glazing around the crew.

The finalists in the competition were Henschel, which proposed a neat single-seater, and Focke-Wulf, which scored because it suggested using a modified version of the Fw 189, which was already being built. The Fw 189 version was very much a compromise, but so was the rival Hs 129, the first prototype of which was flown in February or March 1939. Comparative testing was hampered by the fact that both aircraft were disastrous. They were sluggish in the extreme, and the Hs 129 had such a cramped cockpit that the engine instruments had to be mounted on the inner sides of the engine nacelles, and the control column was so short that great force was needed for even modest manoeuvres.

Opting for the Hs 129

In the end, what tipped the scales in favour of the Hs 129 was that it was smaller and eost only about two-thirds as much as the Focke-Wulf rival. The decision was taken to go ahead with eight pre-production Hs 129A-0 aircraft, and these were all delivered by the time the Blitzkrieg was unleashed in Western Europe on 10 May 1940: They were put through prolonged trials and evaluation programmes and some later equipped the Schlachtflieger training Staffel at Paris-Orly.

Basically, the Hs 129 was a completely conventional aircraft with a simple, stressed-skin structure. The wing, with all the taper on the trailing edge, carried hydraulically driven slotted flaps, and was built as a centre-section integral with the fuselage and two bolted outer panels. The 343.8-kW (465-hp) Argus As 410A-1 air-cooled inverted Vee-12 engines driving Argus automatic controllable-pitch propellers were almost identical to the installations used in the Fw 189, which was already in production. Fuel was housed in a single cell in the fuselage and a tank in each wing inboard of the nacelles. The single-wheel main landing gears retracted backwards hydraulically, part of each wheel remaining exposed to avoid damage in a wheels-up landing.

Where the Hs 129 was unusual was that the fuselage was remarkably slim, with a triangular section (narrow at the top, broad at the bottom), with the front end in the form of a cramped cockpit surrounded by welded armour of 6-mm or 12-mm thickness, and with small panes of glass 75 mm thick. Total weight of the nose armour was 1080 kg (2,380 lb). As already noted, the great wish to minimize overall dimensions severely hampered the pilot's ability to fly a practical ground-attack mission, and for a large pilot made it almost impossible. On the other hand, the aircraft did carry the required armament, there being one 20-mm MG FF cannon in each side of the fuselage (with a prominent blister fairing over the ammunition drum) superimposed over a 7.92-nnn MG 17 machine-gun in the lower flank of each forward fuselage with the breech ahead of the wing spar.

It was obvious to Chief Engineer Dipl. Ing. Fr. Nicolaus that a much better aircraft could be built, using more powerful engines. His team accordingly prepared drawings tot the P.76, a slightly larger aircraft to be powered by two 522-kW (700-hp) Gnome-Rhöne 14M radials, large numbers of which had become available following the defeat of France. It was decided, however, that too much time would be lost in tooling up for a bigger aircraft, and so the final compromise was merely to modify the existing Hs 129A to take the bigger and more powerful French radial engines. Remarkably few modifications were needed, but W one respect the resulting Hs 129B did incorporate a major improvement. The cockpit was modified with large slabs of armour glass to give much better vision, although possibly at the expense of slight increase in vulnerability. The French engines were installed very much in the way used in existing French aircraft, driving three-bladed Ratier electrically-controlled, constant-speed propellers.

Overall, the Hs 129B was a great improvement, although it was still a poor performer. It was slower than the Ju 87D, had a much shorter range and was nowhere near as agile or pleasant to fly, despite contin­ual tinkering with the flight controls which resulted in the addition of fast-acting electric trim tabs.

Operation Barbarossa

After the invasion of the Soviet Union in June 1941, it became evi­dent that the Hs 129 was in principle an aircraft of great importance. In Poland and France the little Hs 123, despite the fact that it was an obsolescent biplane of very limited capability, had demonstrated what the General Staff had previously been reluctant to believe: that aircraft could play a valuable, and even crucial, role in land battles. So the Hs 129B was put into immediate production with high priority. A late change was to replace the MG FF cannon by the much harder-hitting MG 151, occasionally in the high-velocity 15-mm form but usually in 20-mm caliber, with 125 rounds each (the bulges on each side of the fuselage were retained). Provision was also made for the addition of various field modification kits to add specialized weapons or equipment, normally hung either beneath the fuselage or under each outer wing.

The first pre-production Hs 129B-0 was delivered at the end of 1941, but Henschel suffered many severe problems and delays which

seriously held back the build-up of the planned Schlachtgeschwader force. Modifications were continually having to be introduced to rectify faults, equipment and parts were late on delivery, and the planned output of 40 per month was not attained until mid-1943. By far the biggest single problem was the engine, which showed itself to be severely intolerant of either dust on the Eastern Front or, worse, sand in North Africa. Its reliability was extremely poor, and despite the most urgent investigations it took six months to find any sort of real cure. The first Staffel, 4./Sch.G. 1, had a very depressing experience in the push for the Caucasus W mid-1942, while at the end of the year the next unit, 4./Sch.G. 2, suffered a series of disasters in North Africa and was eventually evacuated with no aircraft.

During 1943 the tempo of Hs 129B effort increased greatly, but difficulties in production and high attrition made the actual build-up of Sch.G. units a frustrating process. On the other hand, the combat effectiveness of the aircraft considerably with the fitting of the modification kits, most notably the addition of a huge 30-mm MK 101 gun under the fuselage, with 30 shells. This had a lethal effect against all armoured vehicles except main battle tanks, and even these were sometimes vulnerable when attacked from the rear. Other add-­on loads included an internal camera, a battery of four MG 17 machine-guns or various loads of small bombs, especially boxes of 4-kg (8.8-1b) SD4 hollow-charge bomblets which had considerable armour-penetration capabilities.

A flying gun

Production gave way to the Hs 129B-2/Wa (Waffenträger), the suffix meaning that the very powerful MK 103 gun was fitted not as a field modification but at the factory. The MK 103 had greater anti­tank effectiveness. As an alternative, some aircraft were fitted with a BK 3,7, as used on the very effective Ju 87G. This gun necessitated removal of the MG 17 machine-guns in order to accommodate its ammunition. (Of course, whereas the Ju 87G had carried two of the 37-mm guns, the Hs 129B-2 carried only one.)

The massive build-up in Soviet strength with thick-skimied tanks contrasted with the faltering strength of the Sch.G. units, which continued to be afflicted by poor engine reliability despite the addition of properly designed air filters. The overriding need was for more powerful anti­armour weapons, and on 10 January 1944 a special unit, Erprobungskommando 26, was formed at Udetfeld out of previous Sch.G. units to centralise the desperate effort to devise new weapons

and tactics. Its Hs 129s soon appeared with various new armament, some of which were too much for what was, after all, a small aircraft.

Radical new weapons

The outstanding example of the new weapons was the radically different Forstersonde SG 113A. This comprised a giant tube resembling a ship's funnel in the centre fuselage just behind the fuselage tank. Inside this were fitted six smooth-bore tubes, each 1.6 m (5 ft 3 in) long and of 77-mm caliber. The tubes were arranged to fire down and slightly to the rear, and were triggered as a single group by a photocell sensi­tive to the passage of a tank close beneath. Inside each tube was a com­bined device consisting of a 45-mm armour-piercing shell (with a small high-explosive charge) pointing downwards and a heavy steel cylinder of full calibre pointing upwards. Between the two was the propellant charge, with a weak tie-link down the centre to joint the parts together. When the SG 113A was fired, the shells were driven down by their driving sabots at high velocity, while the steel slugs were fired out of the top of each tube to cancel the recoil. Unfortunately, trials at Tamewitz Waffenprüfplatz showed that the photocell system often failed to pick out correct targets.

Another impressive weapon was the huge PaK 40 anti-tank gun of 75-mm calibre. This gun weighed 1500 kg (3,306 lb) in its original ground-based form, and fired a 3.2-kg (7-lb) tungsten-carbide cored

projectile at 933 m/sec (3,060 ft/sec). Even at a range of 1000 m (3,280 ft), the shell could penetrate 133 mm (5Y4 in)of armour if it hit square-on. Modified as the PaK 40L, the gun had a much bigger muzzle brake to reduce recoil and electro-pneumatic operation to feed successive shells automatically. Installed in the Hs 129B-3/Wa, the giant gun was provided with 26 rounds which could he fired at the cyclic rate of 40 rounds per minute, so that three or four could be fired on a single pass. Almost always, a single good hit would destroy a tank, even from head-on. The main problem was that the PaK 40L was too powerful a gun for the aircraft. Quite apart from the severe

In order to provide a hard-hitting weapon against Soviet tanks, the

Hs 129B-3/Wa was evolved, with a 75-mm Panzerabwehrkanone 40 in a large ventral fairing. Performance and agility were drastically reduced, although one shot could knock out the biggest Soviet tank.

Limited production

In late September 1944, the entire manufacturing programme was abandoned, along with virtually all other German aircraft except for the “emergency fighter programme”. Total production had amounted to only 870, including prototypes. Because of attrition and other problems, the Hs 129 was never able to equip the giant anti-tank force that could be seen to be needed as early as winter 1941-42, and its overall effect on the war was not great. Towards the end, in autumn 1944, operations began to be further restricted by shortage of high­-octane petrol, and by the final collapse only a handful of these aircraft remained.

The Hs 129B equipped the three Staffeln of the 8th Assault Wing of the Royal Romanian Air Corps. On 23 August 1944 there was a coup in Romania, as a result of which the country changed from being an ally of Germany to being an enemy. These Hs 12913s, accordingly, were used against the German armies, finally being combined into a unit equipped with the Ju 87D.

There were plans for a supposedly improved Hs 129 C. It would have been powered by 626.8-kW (840-hp) Isotta-Fraschini Delta IV inverted Vee-12s, giving better performance, and would normally have carried twin MK 103 guns mounted in a kind of turret beneath the fuselage, with a small amount of traverse under pilot control. This version was abandoned because of non-availability of the Italian engines.