Generally speaking, there are three iterations of iconic denim jacket styles, aptly named Type 1, Type 2 and Type 3.

The Type 1 jacket dates as far back as the late 1800's and was originally referred to as the blouse jacket, manufactured for railroad workers and miners across America.
Department stores would each produce their own take on the jacket with some minor differences, but ultimately they shared the same key features: a simple and roomy design, pleats in the back for ease of movement, a cinch back to adjust the fit, and a single pocket on the chest.

The Type 2 jacket came about much later in in 1950's post-war America. A whole new generation of young people were embracing denim thanks to the likes of Elvis Presley and James Dean, transforming something that was once for labourers in to the uniform of rebellious youth. While the Type 2 jacket retained the overall look of the original, it now had two chest pockets, was slightly longer in the body, and the cinch back had been replaced with buttons at the waistband.

The Type 3 arrived just a decade later in 1967, when Levi's designed what is the most common style of denim jacket there is today. A drastic change from its predecessors, it was redesigned in to a much slimmer and longer fit, with chest pockets featuring pointed flaps and V shaped seams sewn on the front to give a narrow more fitted look.