In my day the aircrew knife was called a "Dinghy Stabber" and that was its purpose. The thing you sat on was the packed dinghy in the ejection seat...If while you were airborne the dinghy were to inflate for some reason then it would balloon out between your legs and stuff the stick hard forward...You then needed to draw the dinghy stabber from its sheath on your leg and frantically stab the dinghy to deflate it. All this while experiencing pretty hard negative G and plunging ever more steeply at the Earth!!