Oddly I went shopping for paint today, the gallon can type, and the finishes were matt (flat), egg shell, satin, semi-gloss, gloss, and high gloss. The samples in front of me the egg shell is very slightly glossy, and the satin has a slightly detectable glossy look. Remember we are talking about middle 20th century oil based paint. In the 1970s my parents had the repaint the exterior of their house every other year. The house was last repainted in 2011 and it still looks good as of last fall. The paint back then didn't last. Anything deployed in to a combat zone back then the proper finish should be a light washing with rust.