The HOT (French: Haut subsonique Optiquement Téléguidé Tiré d'un Tube, or High Subsonic, Optical, Remote-Guided, Tube-Launched) is a second-generation long-range anti-tank missile system. It was originally developed to replace the older SS.11 wire guided missile in French and West German service. The design was a collaboration between the German firm Bölkow and the French firm Nord. Bölkow and Nord later merged into MBB and Aérospatiale respectively, both of which then formed Euromissile to design and produce the MILAN, Roland and HOT. This ultimately became part of MBDA. In comparison to the SS.11, HOT has longer range, flies faster, and is semi-automatically guided instead of manually. It has become one of the most successful missiles of its class, with tens of thousands of missiles produced, used by no fewer than a dozen countries worldwide, and validated in combat in several wars. The missile system is also commonly mounted on light and medium armored vehicles, and attack helicopters. HOT entered limited production in 1976, with mass production of 800 missiles a month reached in 1978. HOT initially became operational with the German and French armies fitted to specialized armored antitank vehicles. In addition, Euromissile received large export orders from Middle East nations at the start of mass production. This was likely due to the situation in the late 1970s where many nations did not want to rely solely on arms purchases from the Soviets combined with the U.S. Congress restrictions on the export sales of the TOW antitank missile. In Europe, the end of the service life of the HOT missile system is in sight with the French opting to purchase Hellfire II missiles for their Tiger-HAD attack helicopters and the Germans planning to transition to the PARS 3 LR. Austria has decommissioned its HOT-carrying tank destroyers, while Spain is transitioning to Spike missiles to replace their HOT missile inventory. The HOT missile continues to be in widespread use in other areas of the world. Design and function Project studies by both firms started in 1964, at about the same time the US Army started a project that resulted in the TOW missile. Unlike TOW, which entered service in 1973, the development and testing phase for HOT took considerably longer. The design goal was to produce an antitank missile that could be fired from both vehicles and helicopters; that employed the SACLOS guidance system instead of the less reliable MCLOS system used