Karabin przeciwpancerny wzór 35 (abbreviated "kb ppanc wz. 35"; "anti-tank rifle, model 35"), was a Polish 7.92 mm anti-tank rifle used by the Polish Army during the Polish Defensive War of 1939. It was also known by its code name, kb Urugwaj (kb Ur), or by the name of its designer, Józef Maroszek.
One of the rifle's cover names was "Urugwaj" (hence "Ur"), the Polish name for Uruguay, the country to which the "surveillance equipment" was supposedly being exported.
After the fall of Poland, the German army captured large numbers of the kb ppanc wz.35 and used it as "Panzerbüchse 35 (polnisch)" (abbreviated "PzB 35(p)"). The Italian army also benefitted from the booty and used it under its own designation as "fucile controcarro 35(P)." Both names translate roughly as "Anti-tank Rifle 35 (Polish)."
In early 1940, one of the rifles, its stock and barrel sawed off, was smuggled out of Poland across the Tatra Mountains into Hungary for the Allies by Krystyna Skarbek and Polish fellow couriers. The rifle never saw service with the Allies, however, because the drawings and specifications had been destroyed by the Poles during the invasion of Poland; reverse engineering would have required too much time.
The DS ammunition was based on a standard 7.92 mm bullet as used by both the Mauser rifle Model 1898 (wz.98) and its Polish variant the Karabinek wz.29. The length of the cartridge was extended to 131.2 mm and the overall weight was 64.25 g. After an additional series of tests the copper cartridge case was replaced with a case made of brass (67% copper/ 23% zinc).
Uniquely, compared to other armour-piercing designs, the DS round instead of using tungsten or a similar hard metal for the core had lead in a steel coating, like ordinary rifle bullets. The penetration was not through punching the core through the armor but from the impact of the bullet flattening against the plate, transferring kinetic energy to the metal. The key to success for this technique was a very high bullet velocity. The result was that the bullet was punching a core, about 20 mm in diameter out of the armour, a larger size than the actual rifle caliber. The core would then ricochet inside of an armoured vehicle damaging the engine or killing the crew.
The rifle was based on the Mauser rifle, with the action modified to sustain the higher pressure of the new cartridge and the barrel lengthened significantly. The first tests carried out in Brześć and Pionki showed that the new weapon was capable of penetrating a 15 mm steel plate at a distance of 300 metres with similar results against angled steel plate. Initially the barrel could only sustain up to 30 shots, after which it had to be replaced with a new one. However, this drawback was soon corrected and the final prototype could fire approximately 300 shots. The committee accepted the new design on November 25, 1935, and in December the Ministry of Military Affairs ordered the delivery of 5 rifles, 5000 cartridges and a set of spare barrels for further tests.
After the tests carried out by the Centre of Infantry Training in Rembertów proved the effectiveness and reliability of kbk ppanc wz.35, the Ministry ordered 7610 rifles to be delivered to the Polish Army by the end of 1939. It is uncertain how many rifles were actually produced, but it is often estimated that there were more than 6,500 delivered by September 1939.
The rifle was carried by the leader of the two-man rifle team on a carrying strap. The other member of the squad was his aid and provided him with cover while he was reloading. The weapon was usually fired from prone supported position with the bipod attached to the barrel. However, it could be also used in other positions, like prone unsupported and crouch. The effective range was 300 metres and the weapon was effective against all German tanks of the period (the Panzer I, II and III, as well as the Czech-made LT-35 and LT-38) at 100 meters. At up to 400 meters it could destroy all lightly-armored vehicles. It could penetrate 15 mm of armor, sloped at 30° at 300 m distance, or 33 mm of armor at 100 m. Interestingly, an Italian manual stated maximum penetration as 40 mm.
Despite well-established opinion, the Karabin przeciwpancerny wz.35 was extensively used during the Polish Defensive War of 1939 by most Polish units. After Poland was overrun by Germany and the Soviet Union, large quantities of this weapon were captured. The Germans pressed it into service as Panzerbüchse 35 (polnisch) (PzB 35(p)), and sped up work on their own simplified, one-shot anti-tank rifle Panzerbüchse 39 (PzB 39). According to some sources, however, the Germans replaced the DS bullets in the captured ammunition with their own 7.92 mm hardened-steel-core bullets from the PzB 39.
Also, several features of the Polish rifle, most notably the lock, were used in developing the Soviet PTRD, 14.5 mm anti-tank rifle.