Development of the OA vz. 23:
The PA-II (“Armored Car II”) was developed by Škoda, which capitalized on the experience gained on the previous semi-experimental PA-I, in 1922-23. But, this time, the Chief Engineer’s choice was to provide the hull with an all-around streamlined armor bodywork.
This quickly earned the new vehicle the nickname of “Želva” (Tortoise), never officiated. Instead, the Army designation was Obrněný Automobil model 1923 (OA vz.23). By the fall of 1923, the blueprints were ready and submitted to the the Army. 12 vehicles were ordered, to be delivered from December 1924 and until mid-1925.
Design of the “turtle”
Although the chassis was roughly identical to the experimental PA-I, the armored body was entirely new. It had unusually curved shapes, which seemed like an Art Deco essay, but were dictated by cold considerations of maximal protection effectiveness. Instead of casting the armor, only possible for large thicknesses, the plates were hammer-shaped, 5.5 mm (0.22 in) at the thickest. This was the same process by which the bodywork artists tailored cars for the rich and famous, these skills being present at Škoda as well, descended from a long tradition going back to the master craftsmen shaping knight armor by hand. All the parts were then riveted on a steel frame built above the chassis. The latter was perfectly symmetrical, with the double drive pioneered by the PA-I. The two drivers sat in centrally at either end, and had a twin-fold armored shutter and lateral armored shutters. Access was granted by central doors in the fighting compartment. There was also a provision for four machine guns. These were of the heavy liquid-cooled Schwarzlose MG.08 type, having 6250 rounds. They were mounted in ball-mounts, having some limited elevation/depression and traverse. They were served by the two gunners. A small cupola could be opened for the commander to direct fire from the roof.
The engine was a Škoda, 4 cylinder, 9730 cc, 70 hp, placed in the center, right below the fighting compartment. It gave a maximum top speed, on road, of 70 km/h (44 mph), which was acceptable given the weight of the vehicle. Field performance showed it could ford 1.50 m deep of water, a 30 cm vertical obstacle or cross a trench 45 cm wide. The suspensions and tires were not ideal for cross-country rides, but at least it had four wheel drive. The chassis had the serial numbers from NIX58 to NIX69.