Individual　metallic　nanowires　can　sustain　ultra　large　elastic　strains　of　4-7%.　However,　achieving　and　retaining　elastic　strains　of　such　magnitude　in　kilogram-scale　nanowires　are　challenging.　Here,　we　find　that　under　active　load,　similar　to　5.6%　elastic　strain　can　be　achieved　in　Nb　nanowires　embedded　in　a　metallic　matrix　deforming　by　detwinning.　Moreover,　large　tensile　(2.8%)　and　compressive　(-2.4%)　elastic　strains　can　be　retained　in　kilogram-scale　Nb　nanowires　when　the　external　load　was　fully　removed,　and　adjustable　in　magnitude　by　proceSsing　control.　It　is　then　demonstrated　that　the　retained　tensile　elastic　strains　of　Nb　nanowires　can　increase　their　superconducting　transition　temperature　and　critical　magnetic　field,　in　comparison　with　the　unstrained　original　material.　This　study　opens　new　avenues　for　retaining　large　and　tunable　elastic　strains　in　great　quantities　of　nanowires　and　elastic-strain-engineering　at　industrial　scale.