Excerpt from Charles Bain
There were many types of specialised close-support and ground attack aircraft as far back as the First World War, but this class of aircraft was then virtually ignored until the Spanish Civil War! The fighting in Spain showed, once again, that this category was one of the most important of all.
The Henschel was much more armour, and less powerful engines. (Two 495hp Argus As 410A-1 air-cooled inverted-vee-12s) The pilot, (who was the only person on board) sat in the extreme nose behind a 3-inch thick windscreen, with his cockpit surrounded by armour. The triangular-section fuselage had self-sealing tanks, the guns in the sloping sides and a hardpoint for a bomb underneath.
Test pilots at Rechlin roundly cursed the A-0 pre-production batch as grossly underpowered, but these aircraft were used on the Eastern Front by Germany's Romanian Air Force Allies.
The redesigned B-series used the vast stocks of French 14M engines that were available. (And were then being produced by the Vichy government for the Me323 Gigant.) Altogether, the Germans produced 841 Bs, which were used with considerable success in the East, but with less success in North Africa. The B-1/R1 had two 7.92mm MG17 and two 20mm MG 151/20, along with two 110lb or 48 fragmentation bombs.
The R2 had a 30mm MK 101 clipped underneath itself, and was the first aircraft to use a 30mm gun in combat action. The R3 had a ventral box of four MG 17. The R4 carried up to 551 lb of bombs. The R5 had a vertical camera for photo-reconnaisance. The B-2 series also changed the inbuilt MG 17s for MG 131s and other subtypes that had numerous kinds of armament, including the 37mm BK 3.7 and the vicious 75mm BK 7.5 gun, whose muzzle extended about eight feet ahead of the cockpit. This fearsome weapon, called "Pak" by many, was employed with some success.
The most novel armament, used against the Russian armour forces with often devastating results, was a battery of six smooth-bore 75mm tubes firing recoilless shells down and to the rear with automatic triggering as the aircraft flew over metal objects.
The Henschels were already in operational service by 1944. The New Luftwaffe Schlachtflieger, the specialists close support formations, were an all important element of the Luftwaffe against the Russians. The weapons carried by some Hs129's, could knock out even the mighty Josef Stalin tanks. As with all the weapons of the Luftwaffe, the Hs129s were too late and too little to stave off defeat. Many have speculated however, that the Luftwaffe close-support units delayed the Russians by months. While this may or may not be true, one must give the Hs129 credit where it is due. What it lacked in maneuverability and speed, (the lack of speed making it easier to attack) the Henschel made up in armour and firepower. The Hs129 was also successor to the Hs123, which was finally phased out in 1944, after a service career that lasted since the Spanish Civil War.
If the Luftwaffe had shown more interest in the Hs129 earlier, they possibly could have slowed the massive Soviet offensives of 1944, in what the Russians came to call: "The Year of Ten Victories"
