Spring of 1942 came only a few short months after the start of WWII, and by August, WPB Limitation Order L-85 would take effect to begin the war era restrictions on fashion. With this in mind, it's easy to spot the adoption of styles that required less fabric. Fashion manufacturers had been making a transition into a leaner fashion look since the late 1930's when a new war seemed at hand.
Simple, yet charming dress styles are offered in this Simplicity spring catalog for 1942. The dresses shown here tend to lean towards a classic button front style with an "A" shaped skirt that just covered the knee (about as high as society would tolerate). I have included the full page so you can see that most of the design was in front, and nearly all dresses sport the same simple darted rear view.
In general, these styles are easy to sew and can be adapted from current sewing patterns. Color blocking and contrast buttons gives design interest without using additional fabric. The slender silhouette is due in part to the use of rayon and acetate textiles that have a soft drape, such as crepes and imitation silk weaves. We also know that many women were sewing crisp cottons too.
Using these pattern designs can also help to date vintage fashion from the WWII era. Look for the same silhouette and style details when dating. There also will be a noticeable lack of zippers in dresses and skirts. You will also find that after the war, many women kept this look until they could afford the Dior influenced silhouettes, so dresses like this with longer length skirts are often from the late 40's.