  We study $3d$ $\mathcal{N}=4$ quiver gauge theories with gauge nodes forming
a $D_n$ Dynkin diagram. The class of good $D_n$ Dynkin quivers is completely
characterised and the moduli space singularity structure fully determined for
all such theories. The class of good $D_n$ Dynkin quivers is denoted
$D_\nu^\mu(n)_p$ where $n \geq 2$ is an integer, $\nu$ and $\mu$ are integer
partitions and $p \in \{ \textrm{even}, \textrm{odd}\}$ denotes membership of
one of two broad subclasses. A full assessment of which $\mathfrak{so}_{2n}$
nilpotent varieties are realisable as $D_n$ Dynkin quiver moduli spaces is
provided. Quiver addition is introduced and is used to give large subclasses of
$D_n$ Dynkin quivers poset structure. The partial ordering is determined by
inclusion relations for the moduli space branches. The resulting Hasse diagrams
are used to both classify $D_n$ Dynkin quivers and determine the moduli space
singularity structure for an arbitrary good theory. The poset constructions and
local moduli space analyses are complemented throughout by explicit checks
utilising moduli space dimension matching.
