Wz . 35 anti - tank rifle Karabin przeciwpancerny wzór 35 ( abbreviated " kb ppanc wz . 35 " ; " anti - tank rifle , model 35 " ) , also " Uruguay " , was a Polish 7 . 9 mm anti - tank rifle used by the Polish Army during the Invasion of Poland of 1939 . It was also known by its codename " Uruguay " ( kb Urugwaj ) ( kb Ur ) , or by the name of its designer , Józef Maroszek . Secrecy and confusion . The weapon was initially a top secret of the Polish Army , and was also known by various codenames . Until mobilization in 1939 , the combat - ready rifles were held in closed crates enigmatically marked : " Do not open ! Surveillance equipment ! " One of the rifle ' s cover names was " Uruguay " ( Polish : " Urugwaj " , hence " Ur " ) , 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 benefited 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 courier s . 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 . Description . In appearance it resembled a rifle with a longer - than - normal barrel supported by a bipod at the front of the wooden stock . It was a bolt - action rifle , fed from a 4 - round box magazine . The barrel was equipped with a muzzle brake to limit the recoil . The brake absorbed approximately 65 % of the shot energy and the recoil was comparable to the standard Mauser rifle , even though the cartridge carried more than twice the amount of propellant . It had fitted iron sights fixed for a 300 - meter range . Unlike other anti - material rifles of the time , the wz . 35 did not use an armour - piercing bullet with a hard core , but rather a lead core , full metal jacket bullet weighing 14 . 579 g ; due to the high muzzle velocity this was effective even under shallow angles , as instead of ricocheting , the bullet would " stick " to the armour and punch a roughly 20 mm diameter hole . Calculated kinetic energy , by shot , before brake was about 11 , 850 J . The high energy was due to the relatively long barrel , and nitro powder giving a muzzle velocity of 1 , 275 m / s . History . Ammunition . In the late 1920s the Polish General Staff started the development of a light anti - tank weapon for the Polish infantry . In 1931 Lt . Colonel Tadeusz Felsztyn from the Institute of Armament Technology in Warsaw started the first tests of various low - calibre cartridges . After the tests of German - made Hagler bullets proved the possibilities of that type ammunition in perforating steel plate , the National Ammunition Factory in Skarżysko - Kamienna was ordered to develop its own 7 . 92 mm cartridge with a muzzle velocity of over 1 , 000 meters per second . After a series of tests , the new " DS " cartridge was proposed . Visit for a picture of the ammunition . The " DS " ammunition was based on a standard 7 . 9 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 and the overall weight was . 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 , as with standard ball , but with a steel jacket . 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 spall , about 20 mm in diameter , out of the armour , a size larger than the actual rifle caliber . The fragment would then ricochet inside of an armoured vehicle , possibly damaging the engine or killing the crew ( an effect similar to that of a modern HESH tank round ) . Rifle . Simultaneous to the development of the ammunition , a young graduate of the Warsaw University of Technology , Józef Maroszek was ordered to design an anti - tank rifle . On August 1 , 1935 , the Committee of Equipment and Armament officially ordered the rifle and in October the first tests of the new weapon started . The rifle was based on the Karabiner 98k , 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 . Use . The rifle was the main anti - tank weapon of an infantry platoon . Each infantry company and cavalry squadron was to be equipped with three rifles , each operated by a team of two soldiers . Additional anti - tank teams were to be created at a later stage . Although the weapon was successively introduced to the units , it remained a top secret . The rifles were kept in closed wooden crates , each marked with a number and a notice " do not open ; surveillance equipment " . The teams were trained in secret military facilities just before the war , beginning in July 1939 , and had to swear to preserve the secret . 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 aide 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 penetrate 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 . Panzerbüchse 35 ( p ) . Despite well - established opinion , the " Karabin przeciwpancerny wz . 35 " was extensively used during the Invasion of Poland 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 . In 1940 , Germany sold some 800 Polish antitank rifles to the Italian armed forces , which used them in combat until the end of World War II . Survivors . The number of surviving . wz 35 rifles is unclear ; it has often been claimed that only four specimens survive , which were exported to the United States in the 1950s . However , there are at least two more in the United Kingdom . One is on exhibit in Poland , at Warsaw ' s Polish Army Museum ; another is located in Armament Museum in Poznań Citadel . The . wz 35 has recently been appraised in England at $ 130 , 000 .