  Let $p$ be a prime and let $G$ be a finite group. By a celebrated theorem of
Swan, two finitely generated projective $\mathbb Z_p[G]$-modules $P$ and $P'$
are isomorphic if and only if $\mathbb Q_p \otimes_{\mathbb Z_p} P$ and
$\mathbb Q_p \otimes_{\mathbb Z_p} P'$ are isomorphic as $\mathbb
Q_p[G]$-modules. We prove an Iwasawa-theoretic analogue of this result and
apply this to the Iwasawa theory of local and global fields. We thereby
determine the structure of natural Iwasawa modules up to (pseudo-)isomorphism.
