with the missile in flight", about 20% of the operational V-2 launches were beam-guided. The Operation Pinguin V-2 offensive began on 8 September 1944, when (English: 'Training and Testing Battery 444') launched a single rocket guided by a radio beam directed at Paris. Wreckage of combat V-2s occasionally contained the transponder for velocity and fuel cutoff. The painting of the operational V-2s was mostly a ragged-edged pattern with several variations, but at the end of the war a plain olive green rocket was also used. During tests the rocket was painted in a characteristic black-and-white chessboard pattern, which aided in determining if the rocket was spinning around its longitudinal axis. The original German designation of the rocket was "V2", unhyphenated – exactly as used for any Third Reich-era "second prototype" example of an RLM-registered German aircraft design – but U.S. publications such as Life magazine were using the hyphenated form "V-2" as early as December 1944. Testing The first successful test flight was on 3 October 1942, reaching an altitude of . On that day, Walter Dornberger declared in a speech at Peenemünde: Two test launches were recovered by the Allies: the Bäckebo rocket, the remnants of which landed in Sweden on 13 June 1944, and one recovered by the Polish resistance on 30 May 1944 from Blizna and transported to the UK during Operation Most III. The highest altitude reached during the war was (20 June 1944). Test launches of V-2 rockets were made at Peenemünde, Blizna and Tuchola Forest, and after the war, at Cuxhaven by the British, White Sands Proving Grounds and Cape Canaveral by the U.S., and Kapustin Yar by the USSR. Various design issues were identified and solved during V-2 development and testing: To reduce tank pressure and weight, rapid flow turbopumps were used to increase pressure. A short and lighter combustion chamber without burn-through was developed by using centrifugal injection nozzles, a mixing compartment, and a converging nozzle to the throat for homogeneous combustion. Film cooling was used to prevent burn-through at the nozzle throat. Relay contacts were made more durable to withstand vibration and prevent thrust cut-off just after lift-off. Ensuring that the fuel pipes had tension-free curves reduced the likelihood of explosions at . Fins were shaped with clearance to prevent damage as the exhaust jet expanded with altitude. To control trajectory at liftoff and supersonic speeds, heat-resistant graphite vanes were used