These machines were manufactured in the Singer Bridgeport Connecticut plant that was bought from Wheeler & Wilson, hence the "W" in the designation. They were also made in black, and a tan combination. The period of manufacture was very short, from 1955 to 1957. There are no date records available. The five levers on the top of the machine control the various built-in zigzag functions, and remind me of old typewriter keys. The machine also uses flat black cams for additional stitch patterns. It uses an odd size needle designated "206".
This particular machine came in a portable case but I’d hardly call it portable…. It weighs a ton! The belt, cords and foot controller are also green.