As CBurr mentioned, 1940s fashion was influenced by WWII. The military style influenced fashion, with women's dresses having square shoulders and military style trim and colors. Sailor dresses were a popular look. Hats also emulated the military style. Underneath their dresses, woman wore "waspies" which were like corsets. A thin waist with broad shoulders was the fashionable look. Women wore their hair curled and shoulder length or longer. Many Rosie-the-Riveter types (women working in factories) tied their hair back in turbans. Because of the wartime shortages, women did not embellish their dresses with many trims, instead they accessorized with their purses, hairstyles, high heels, and bright red lipstick.
I can tell you from personal experience, because I wore my mother’s wedding dress! The dress – from the early ‘40s – had padded shoulders. Since I have broad shoulders, I had the pads removed! :-)
Of course, fashion was greatly affected by the fact that we were in the middle of World War II and many fabrics and accessories were either scarce or completely unavailable. For example, silk and nylon were scarce because they were used to make parachutes. As a result, many women drew lines up the backs of their legs since they couldn’t get the seamed nylons of the day.
Read this site for lots and lots of details!
Pick up this months issue of Brides. They are celebrating their 75th anniversary tipping their hats to the vintage styles of wedding past. One hot trend for the late 40s early 50s I saw were sweetheart necklines, scalloped detailing, and other intricate detailing with buttons and bows. All of which are making a big comeback in modern designs.