Vietnam Era Bouyant Flight Pilots Bomber Jacket Military Issued

In the event of a water landing one would float in this jacket. Not sure what the API 41 means however. On the tag there is a contract number and within that number is the year issued being "68". Its super heavy duty the tag states this is for extreme cold weather. Also the bouyancy liner can be removed. Ive handwashed this as there were some spots and I got those out. Its no big deal to handwash and it dries quickly but it will take a machine wash too. Tag has washing instructions. The tag says the jacket is a large 42-44 but I measured the chest at 52" right under the armpits and bombers are not designed to be skin tight but 52" tells me XL....quandry.