The real post-war design history at Cadillac begins with the development of the model for  1948. When World War II came to an end, Cadillac was a bit out of control. A few key figures who normally make important decisions were not even there.  

The 1948/1949 Cadillac was a dream come true, a  dream from the 20s of a young man. Years earlier, his well-known Detroit mother, Clara, had bought the third Cadillac ever built, in 1903. Henry Leland, Clara's girlfriend's husband and Cadillac founder, had borrowed his own driver to teach her how to drive. Since that time, there has been a long succession of new Cadillacs in the woman's life. So the boy had literally grown up with Cadillacs. Clara's 1918 Phaeton had something that sparked the boy's appreciation for design. When his mother sold the Phaeton after moving to California, the boy was sad. He started sketching it and then expanded that into the creation of his own car designs. He promised himself that one day he would design a Cadillac. That boy grew up to be one of the most influential car designers of all time: Franklin Q. Hershey.

An interview with  Hershey talks about how Hershey got to work at GM. It starts with a story about one of his designs:

This was my first serious attempt at drawing a car. I had always been a car lover and finally decided to make a design. We lived in Eagle Rock, California, near Occidental College, where I studied. Just before Christmas 1927, my mother's financial adviser, Mr. Johnson, happened to be at our house. He saw the drawing, was impressed and said, "Why don't you go to Murphy's and ask about Frank Spring, maybe he'll give you a job." I did, and Mr. Spring, the manager, said, "Sorry, you're no good, we can't use you." Mr. Johnson and Mr. Murphy were personal friends, however, and on Mr. Johnson's advice, Mr. Murphy instructed Frank Spring to hire me, which he did, stating, "You're not very good, but we'll see how long you stay.”

Well, in two months I did all their design work. When Murphy went bankrupt (both Frank Spring and I had already gone to Detroit), Frank made me head designer at Hudson. I just didn't feel at home with Hudson and, thankfully, after about two months, I got a call from Harley Earl to come to GM to run the Pontiac studio. After that, Frank Spring and I and our wives became very good friends.

Hershey thus learned the car design trade at the Walter M. Murphy Body Company in Beverly Hills, California, where he designed special bodies for movie stars and millionaires. At General Motors in Detroit, he developed a Bentley-style radiator for Pontiac, which quickly earned Hershey the recognition and support of Harley Earl, GM's design czar. That was followed by the famous Silver Streak Pontiacs in 1933, a design theme that lifted the brand out of its commercial depression and became the brand's trademark for over two decades.

With the approval of GM's German division, Harley Earl established a new studio in 1937. Strother MacMinn, John Coleman, George Jergenson and Frank Hershey as manager and Hans Mersheimer from Opel as design liaison chief. As early as 1936 Franklin Hershey was commissioned to design the "new Kapitän for Opel in Germany". He worked closely with Karl Mersheimer of Opel who had more experience with self-supporting bodies in which Opel was one of the pioneers (with Lancia and Citroën) in Europe. In 1938 Franklin Hershey helped Opel to get the Opel Kapitän ready for production while redesigning the Opel Kadett.

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Just before World War II, he returned to the USA from Germany, where he had worked with GM's Opel and Holden factories, among others. Hershey was appointed head of the General Motors Advanced Design Studio at 40 Milwaukee Avenue in Detroit. One day in the late 1930s, Earl received government permission through a friend to take some of his best designers to Michigan's Selfridge Field to view a secret military aircraft. Designers Bill Mitchell and Frank Hershey belonged to this group. Though no one knew about it at the time, this excursion was destined to become legendary in the history of automotive design. On the runway was the thirteenth Lockheed P-38 Lightning, the aviation marvel that, after further development, would set records in the coming war. The radical design opened Mitchell's, and especially Hershey's, eyes, seeing possibilities they hadn't thought of before, they were fixated by the elegance of the aircraft's design. When the story of the '48 Cadillac is told, the influence of the aircraft's tail fin is usually the predominant theme. Hershey immediately saw fins of sea creatures. Fins were wondrous creations of nature, beautiful, slender, shiny, streamlined and symmetrical, depicting speed, maneuverability and stability, all that a modern car stood for.  However, the effect of the aircraft design was much more than that. Mitchell said, “You have to understand the value of what we saw in the design of that plane. We saw that you could line up from the hood all the way to the tip of the tail, so you could have one clean smooth line.”  Hershey was also impressed with the aircraft's aerodynamic shape,  when he returned to the studio he started experimenting with the tail fin line he had seen. He worked on that idea, but both he and Mitchell moved on to other design projects before leaving GM to serve in the Navy during WWII.

Still, the encounter with the P-38 Lightning had a magical effect on all the designers who had seen it. This magic would survive the long war until the introduction of the 1948 Cadillac, nearly a decade later. It was the new definition of "taste" for the Cadillacs of the years to come.  Hall Hibbard and Kelly Johnson, the designers of the plane that German pilots would later call der Gabelschwanz, the fork-tailed devil, were quite modest about their influential design. The plane got its shape because it had to accommodate two liquid-cooled GM Allison engines, each with a General Electric turbocharger and Prestone radiators. Johnson was quoted in historian Bill Yenne's book on Lockheed: "There was a reason for everything there was, a logical evolution, the form came naturally. In design you are forced to develop unusual solutions to unusual problems." In other words, the design of the aircraft followed the functional requirements imposed on the designers by the military. It is one of those interesting coincidences in history that the Cadillac Motor Division manufactured precision parts for the Allison engines used in the P-38 during the war. Cadillac even took advantage of this fact in its wartime advertisements.

Hershey returned to GM in 1944 and Earl put him in charge of the Cadillac Design Studio. As the war subsided, Cadillac had to be primed for a return to civilian production. Mitchell, who previously led the Design Studio, didn't leave the Navy until about a year after Hershey. Even then, he didn't stay with GM for long because he was asked to run a private design firm that Harley Earl had previously founded with his sons. Both the 1948 and '49 Cadillacs were designed before Mitchell finally returned to GM.

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There is another important fact. In the late 1930s, Earl had asked the University of Michigan at Ann Arbor to find out what the optimal size would be for a small clay model of a car. Earl's idea was to save time, money and space while allowing his designers to create models that would give a good idea of the look of a design. The answer was a scale of 3/8.

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The concept "Interceptor" was the first design to use the 3/8 scale model concept and show influences from the visit to the P-38 Lightning. Some concepts showed an early version of the tail fin, others did not. However, they were all based on the single line that flowed from the front edge of the vehicle to the rear bumper. Some of the Interceptor models were even triple pleated like the P-38 and relied heavily on the aircraft's design. Hershey remembers one day in the studio at the GM development center working on the clay models and adding fins to a particular model from that series. When Earl walked in with Nick Dreystadt, one of the top executives, he saw them and said to Hershey, "Take those things off!" Being the tough individualist that he was, Hershey left the fins on and covered them with a sheet. Earl came back a few days later and said the same thing: "Goddamn it, I told you to take those things off. If they don't come off tomorrow I'll fire you!" Hershey capped them off again. Some time later, Dreystadt came into the studio with Earl and a few other people, looked at the model and said, "Thank God, you left the fins on! The big bosses love it!" Earl then encouraged Hershey to apply the fins where he wanted. Tail fins had gained a foothold in Cadillac designs.  

The Interceptor concepts were an interesting side-step of Cadillac styling that was never introduced to the public. Two full-fledged versions of the concept were built shortly after the war. Thanks in part to their aerodynamic design, their ride on the GM test track was spectacular, Hershey recalls. The engineers were especially impressed. The cars were designed at the end of the war and the styling team thought cars should look like airplanes with wings, panoramic windows, air intakes, covered wheels and bullets on the bumpers.

The problem was that top management concluded that their design was simply too progressive for the public. Harley Earl once said, "A fundamental point we've learned...is not to take too big a step, but we do take a risk every now and then." Producing the interceptor was considered too great a risk. Harley wasn't happy with the high, fat-looking sidelines. He seems to have told the big bloated thing to rot. He decided to introduce the styling elements piece by piece. Finnish in 1948, panoramic window in 1953 on the Eldorado, and the roofline was seen in the mid-'50s on Chevys and Pontiacs. After years of speculation, it has become obsolete what happened to the models. They were used in 1957 for crash tests at the Proving Grounds. A promising model has thus come to an end as a test dummy.

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Earl ordered Hershey, as head of Cadillac Design, to break new ground. The 1946 and '47 Caddys were just modified '41 and '42 versions. It was concluded that Cadillac needed a new model, one that would reinforce the leadership position of perfection and design. At this crucial point an important event occurred.

In Detroit, and therefore also at GM, there were many problems with the employees just after the war and therefore many strikes. This prevented the design team from entering the studio. However, while working on the Interceptor, Hershey had purchased a 24-acre farm, 31 miles outside of Detroit, near the General Motors test track. Due to the inaccessibility, he decided to move the Cadillac design team, including his master clay sculptor, Chris Kline, to the ranch to continue design work in the basement. Fortunately, there was a lot of camaraderie in this makeshift facility - and even more hard work. Thus, Hershey's ranch became the birthplace of the famed 1948 Cadillac. Franklin Q. Hershey, the man who would give us the classic Ford Thunderbird just seven years later, was also the man who gave us the '48 Caddy, his childhood dream of designing a Cadillac had come true. But it was more than that, because the '48 would set a design standard that would influence Cadillac for years to come. True fins are a spout of the fender itself; sometimes the rear light is incorporated, sometimes not. The success of the '48 Cadillac tail fin was how Hershey incorporated what Mitchell had learned from the P-38: The fin was a continuation of the flowing front-to-back line. It was actually simple and elegant, but only Hershey had the talent and insight to design it.

The '48 Cadillac was an instant success with buyers. When the dealers first saw him, they were concerned that the buyers would see him  wouldn't like it. But any negative views from the dealers were soon overshadowed by massive public demand. The '48 was the P-38 Lightning on wheels and for sale in every Cadillac showroom. In 1948 Cadillac was DE  luxury car to own.

Everyone wanted to copy the Caddy. Mail order companies had a brisk trade with tail fins that could be mounted on the rear fenders of Fords or Chevys. Design studios around the world designed fins for every car that was facelifted. Eventually, fins could be seen on everything from the Henry J to a Mercedes. Despite the fresh new look, the '48 Cadillac still had many things that had remained distinctive. The name in script, the goddess on the hood, "V" decal on the front, eggcrate grille, "sombrero" wheel covers, and small "Dagmar" bumper protectors. It screamed "Cadillac".  The Dagmars started out simply as grenade holder bumper protectors and later became an important part of Cadillac's style. The name Dagmar is named after NBC's first female TV star, her real name was Virginia Ruth Egnor (1921-2001).

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The Series 61 and 62 were shorter than the same models of the previous year and were available as a two-door fastback club coupé (Sedanet). The 1948-49 coupes were arguably the most beautiful post-war fastbacks. The Fleetwood Series 75 was produced in limited numbers and fitted with '46 sheet metal to be able to amortize the pre-war presses. They demanded awe-inspiring reverence from those who witnessed the glide along one of the boulevards of post-war America.  While the two-piece windshield on all models except the 75 retains a narrow center pillar, it is curved, a 1948 novelty. And because the different models differed in height, Cadillac had to produce four different windshields for the model year. Despite all the new styling features, the 150 hp L-head V8 and Hydra-Matic were adopted almost unchanged from 1941-47. Reliable, smooth and with an excellent reputation, the V8 was as good or better than anything the competition offers. However, he was clumsy and heavy. The performance was adequate. A top speed of 93.3 miles (150 km) per hour, 0-60 mph in 16.3 seconds, and fuel economy of 14 miles per gallon at 60 mph (all figures with Hydra-Matic). The '48 Caddy didn't go into production until the end of February 1948 and was sold in dealer showrooms in March. The model year thus encompassed a short nine months. Demand exceeded supply, but there was only time to build 52,706 cars for model year '48.