The　active　aircraft　defense　problem　is　investigated　for　the　stochastic　scenario　wherein　a　defending　missile　(or　a　defender)　is　employed　to　protect　a　target　aircraft　from　an　attacking　missile　whose　pursuit　guidance　strategy　is　unknown.　For　the　purpose　of　identifying　the　guidance　strategy,　the　static　multiple　model　estimator　(sMME)　based　on　the　square-root　cubature　Kalman　filter　is　proposed,　and　each　model　represents　a　potential　attacking　missile　guidance　strategy.　Furthermore,　an　estimation　enhancement　approach　is　provided　by　using　pseudo-measurement.　For　each　model　in　the　sMME,　the　model-matched　cooperative　guidance　laws　for　the　target　and　defender　are　derived　by　formulating　the　active　defense　problem　as　a　constrained　linear　quadratic　problem,　where　an　accurate　defensive　interception　and　the　minimum　evasion　miss　distance　are　both　considered.　The　proposed　adaptive　cooperative　guidance　laws　are　the　result　of　mixing　the　model-matched　optimal　cooperative　guidance　laws　in　the　criterion　of　maximum　a　posteriori　probability　in　the　framework　of　the　sMME.　By　adopting　the　adaptive　cooperative　guidance　laws,　the　target　can　facilitate　the　defender＇s　interception　with　the　attacking　missile　with　less　control　effort.　Also,　simulation　results　show　that　the　proposed　guidance　laws　increase　the　probability　of　successful　target　protection　in　the　stochastic　scenario　compared　with　other　defensive　guidance　laws.