Danny,
the chains were the a/c standard 10000lb tie down chains. My previous reply was less than precise. They were laid on the seat pan usually and the cushions were placed on top. It was hope that anything that got through the chains would be further retarded by the thick uncomfortable cushion.
For a long time it was the only 'protection' we had. When 'flak' vests became available you then had the choice of wearing it or sitting on it a la the chains.
Or you could use the chains and the vest.