"WEP" is a misnomer. It's not a "WEP" Jacket, that name arose due to tags having the contract authority delineated so you can find jackets that say WEP (Bureau of Weapons or BUWEP) or AER (Bureau of Aeronautics or BUAER) or finally DSA (Defense Supply Agency...created in 1962 and transitioned to DLA in 1978).
Calling it a "WEP" jacket would be like calling it an AER or DSA jacket. It would be more accurate to call it a Poopie Suit Liner or by its real name Winter Flying Suit Jacket (WFSJ). But WEP was picked up by manufacturers who didn't know better soooo...(
http://www.uswings.com/wep.asp)As BB604 attests and Catmandu confims with his tag :
JACKET, SUITS, FLYING, WINTER
Specification MIL-S-18342C
KINGS POINT MFG. CO, INC.
CONTRACT NO. DSA 100-70-C-0345
SIZE 40 R -3-
Sample tag