Hagel had at least one unique quality that no other SecDef has ever had - he served in combat as an enlisted soldier, receiving two Purple Heart medals while an infantry squad leader in Vietnam.
Points against him were: the only Republican in Obama's cabinet; he had reportedly "gotten tired of Obama's micromanaging of military operations".
The second point invites comparisons with Lyndon B. Johnson (36th President of the US, 1963-68) - who famously bragged “Those boys can’t hit an outhouse without my permission”.