The anatomy of nuclear fission---a complex many-body process that has challenged precise modeling for decades---is explored via a comprehensive inverse-kinematics experiment. A Coulomb-fission measurement of relativistic ${}^{234,235}$U and ${}^{237,238}$Np projectiles at the GSI R3B/SOFIA setup has provided some of the most precise fission-fragment yields yet for these uranium isotopes and the first isotopic yields for two neptunium isotopes. The data precision and the extensive comparisons aim to confirm certain previous hypotheses regarding the fission process and to refute others.