found to be insufficient, forcing the crews to wear protective masks inside their tanks, thus greatly reducing the crews' performance. The experts also found that the gearbox did not allow for shifting into reverse while the vehicle was moving, forcing the crew to stop the tank before reversing. To make things even worse, the radios used in the tank tended to interfere with the turret control system, resulting in uncontrolled turret movements whenever the radios were used at full power. A year before the Weltwoche article, another very dangerous fault was found. Switching on the heating system could lead to the main gun firing the round in the gun. This problem was caused by some systems sharing the same electrical circuits. This problem never led to any accidents. In a sarcastic headline, Swiss tabloid Blick commented: "The Panzer 68 is much more dangerous than it seems!" Most of the problems were resolved with the upgrade to the 68/88 model. Variants Panzer 68 1st Series (Pz68); 170 built 1971–1974, all upgraded to Pz68 AA 2 in 1975-1977 Panzer 68 2nd Series (Pz68 AA 2); 50 built 1974-1977; one equipped with a new turret and updated as the Pz68/88 Panzer 68 3rd Series (Pz68/75); also named Pz68GT (Grosser Turm ("Bigger Turret")); 110 built 1978–1979, all upgraded to Pz68/88 in 1993 Panzer 68 4th Series (Pz68/75); 60 built 1983–1984, all upgraded to Pz68/88 in 1993 Panzer 68/88; upgraded Pz68 AA 2 with modern laser guidance system (which was borrowed from the Pz 87 Leopard), an improved commander entry and updated camouflage pattern. Majority of aforementioned technical issues fixed. Panzer 68-2000 (Pz68-2000); project, fitted with 120mm Smoothbore gun, modern thermal sights and electronics, more powerful engine, new angular turret with highly improved NBC protection, additional protection. Rejected in favor of the Panzer 87 Leo due to high developing costs. Derivative vehicles Entpannungspanzer 65 Recovery Tank 65 - vehicle recovery variant. Panzerartilleriekanone 68 Brückenpanzer 68 Bridge Tank 68 - bridge-laying variant, with single-piece span instead of more common scissors bridge, capable of spanning gap; 30 produced between 1974 and 1977 and used until 2011 Fliegerabwehrpanzer 68 Anti-aircraft Tank 68 - variant fitted with Flakpanzer Gepard turret, mounting two Oerlikon 35mm anti-aircraft guns, on Panzer 68 hull widened by ; two tanks modified and tested in 1979-1980, not placed into production Zielfahrzeug 68 Target Vehicle 68 - mobile target for training troops in the use of