having been formally stamped with production build numbers. All six were homologation tested, certified, registered, and licensed as bespoke, coachbuilt cars. The prototype seemingly vanished without a trace. It was finally recognized in 2012, when it was discovered that the Type 178 chassis, stamped as 820001, was the long lost "missing link". After World War II, the second-generation 4.5-litre series was to address the export market, ostensibly in North America, under the five-year economic revitalization strategy known as the "Pons Plan". Delahaye's second generation 4.5-litre engine was an overhead-valve, inline, six-cylinder, similar to the preceding Type 135 in format, but a litre larger in displacement. It was an improvement over the successful Type 135 engine, in having seven main bearings versus four, and a twelve-port instead of nine-port cylinder-head. Unlike the cast-iron block and head of prior models, the 4.5-liter engine had a cast-aluminum block, and cast-iron head, separated by a copper and asbestos head-gasket. The standard compression ratio was 6.5:1, but that was enhanced in the optional Type 175S, that was fitted with three Solex carburetors, instead of one; and, wire wheels. By 1946, those familiar with Delahaye knew of the six pre-production units. But those six excluded the developmental experiment that was presented to the shareholding directors in March 1944 by Charles Weiffenbach, in the unavoidable absence of chief design-engineer Jean Francois, for production approval. The prototype remained unidentified. It was superseded when the first and second pre-production units (reference numbers 90001 and 91001) were sequentially fabricated in late 1945, in Type 275S specification. The 1946–49 Paris Auto Salon Type 175S show-chassis was the fourth of the six built, but was not operational, there being no fuel-line, electrical equipment, mechanical linkages, and switches. Chassis The new 175/178/180 series chassis introduced the semi-monocoque concept. These units were completely different from the foregoing Type 135 and its several longer wheelbased iterations, in width, proportions, and structure. The stressed-steel floor-pan, welded integrally around the bottom perimeter of the passenger compartment. The chassis was dramatically larger, and heavier, than the Type 135. It had parallel side-rails, and these longitudinal members were boxed, instead of open channels. Type 135,145, 148L, and 165 frame-rails tapered from the aft cockpit cross-member forward, whereas the three new models' cockpits were parallel-sided rectangles, setting the precedent. The Types 135,145,148,155, and 165 had the identical,proprietary, independent front suspension system shared with Delage, and Talbot. In contrast, the all-new