  We realize four-dimensional N=2 superconformal quiver gauge theories with
alternating SO and USp gauge groups as compactifications of the six-dimensional
D_N theory with defects. The construction can be used to analyze infinitely
strongly-coupled limits and S-dualities of such gauge theories, resulting in a
new class of isolated four-dimensional N=2 superconformal field theories with
SO(2N)^3 flavor symmetry.
