Study sought to survey 108,000 people , only 24 % responded . Defense department extrapolated figures from results . Source : ` ` list of most serious challenges '' for the armed services . Air Force officials faced tough opposition from senators .
Study sought to survey 108,000 troops , only 24 % responded . Defense department extrapolated figures from results . Hagel : `` One of most serious challenges '' for the armed services . Air Force officials face tough questions from senators .