PWS-6
... that the PWS-6 was the first Polish aircraft fitted with slats—but the prototype is the only model ever produced?
... that the <b id="mwGyo"><a href="./PWS-6" id="mwGys" rel="mw:WikiLink" title="PWS-6">PWS-6</a></b> was the first Polish aircraft fitted with <a class="mw-redirect" href="./Leading_edge_slats" id="mwGyw" rel="mw:WikiLink" title="Leading edge slats">slats</a>—but the prototype is the only model ever produced?