The Collaborative International Dictionary of English v.0.48:

Air jacket \Air" jack`et\
   A jacket having air-tight cells, or cavities which can be
   filled with air, to render persons buoyant in swimming.
   [1913 Webster]

WordNet (r) 3.0 (2006):

air jacket
    n 1: an inflatable life jacket [syn: Mae West, air jacket]