D\'{e}vissage Hermitian Theory

We prove D\'{e}vissage theorems for Hermitian $K$ Theory (or $GW$ theory), analogous to Quillen's D\'{e}vissage theorem for $K$-theory. For abelian categories ${\mathscr A}:=({\mathscr A}, ^{\vee}, \varpi)$ with duality, and appropriate abelian subcategories ${\mathscr B}\subseteq {\mathscr A}$, we prove D\'{e}vissage theorems for ${\bf GW}$ spaces, $G{\mathcal W}$-spectra and ${\mathbb G}W$ bispectra. As a consequence, for regular local rings $R$ with $1/2\in R$, we compute the ${\mathbb G}W$ groups ${\mathbb G}W^{[n]}_k(Spec{R})$ forall $k, n\in {\mathbb Z}$, where $n$ represent the translation.