Hs 129 B-1
Even before the A-1s were delivered the plane was redesigned with the Gnome-Rhône 14M radial engine, which were captured in some number when France fell. This engine supplied 700 hp (522 kW) for takeoff compared to the Argus at 465 hp (347 kW). The Gnome-Rhone radials were also made in versions with opposite rotation for the propeller, and were installed on the Hs 129 with the port engine rotating clockwise, and the starboard rotating counterclockwise, as seen from nose-on, thus eliminating engine torque problems. The A-1 planes were converted into Hs 129 B-0s for testing (although some claim that some As were sold to Romania) and the pilots were reportedly much happier. Their main complaint was the view from the canopy, so a single larger windscreen and a new canopy with much better vision were added, resulting in the production model Hs 129 B-1.
B-1s started rolling off the lines in December 1941, but they were delivered at a trickle. In preparation for the new plane, I./Sch.G 1 had been formed up in January with Bf 109 E/Bs (fighter-bomber version of Bf 109 E) and Hs 123s, and they were delivered B-0s and every B-1 that was completed. Still, it wasn't until April that 12 B-1s were delivered and its 4th staffel (squadron) was ready for action. They moved to the eastern front in the middle of May, and in June they received a new weapon, the 30 mm MK 101 cannon with armor-piercing ammunition in a midline pod.
Hs 129 B-2
By May 1942 after only 50 of the planes had been delivered, they started to deliver the new Hs 129 B-2 model side-by-side with the B-1. The only difference between the two were changes to the fuel system – a host of other minor changes could be found almost at random on either model. As time went on these changes were accumulated into the B-2 production line until you could finally tell them apart at a glance, the main differences being the removal of the mast for the radio antenna, the addition of a direction-finding radio antenna loop, and shorter exhaust stacks on the engines.
In the field the differences seemed to be more pronounced. The R-kits were renumbered and some were dropped, and in general the B-2 planes received the upgraded cannon pack using a MK 103 instead of the earlier MK 101. These guns both fired the same ammunition, but the 103 did so at almost twice the rate.
Hs 129 B-3
Close up of the Bordkanone BK 7,5 cannonEven by late 1942 complaints started about the effectiveness of the MK 103 against newer versions of the Soviet T-34 tanks. One obvious solution would be to use the larger Bordkanone BK 3.7 37 mm gun, adapted from an anti-tank gun that had recently been abandoned by the army. These guns had already been converted into underwing pod-mounted weapons for the Ju 87 and found to be a fearsome weapon. When mounted on the Hs 129 the empty area behind the cockpit could be used for ammunition storage, which would address the only problem with the Ju 87's mounting, a limited ammunition supply.
But for some reason the Luftwaffe decided to skip over this gun for the Hs 129, and as had been done with the heavy-gunned Ju 88P-1, they installed a gigantic 75 mm gun from the Panzer IV to produce the Bordkanone BK 7.5 model. A huge hydraulic system was used to damp the recoil of the gun, and an auto-loader system with twelve rounds was fitted in the large empty space behind the cockpit. The resulting system was able to knock out any tank in the world, but the weight slowed the already poor performance of the plane to barely flyable in this new Hs 129 B-3 version.
B-3s finally started arriving in June 1944, and only 25 were delivered by the time the lines were shut down in September. A small number were also converted from older B-2 models. In the field they proved deadly weapons, but with only 25 of them they had no effect on the war effort.
Hs 129 C
In order to address the poor performance of the aircraft, plans had been underway for some time to fit the plane with newer versions of the Italian Isotta-Fraschini Delta engine that delivered 850 hp (634 kW). However the engine ran into a number of delays, and was still not ready for production when the plant was overrun by the Allies in 1945.
The Hs 129 never really had a chance to prove itself in any way; the plane was produced only in small numbers and deployed during a time when the Luftwaffe was unable to protect them from attack.