  We consider three-dimensional inviscid irrotational flow in a two layer fluid
under the effects of gravity and surface tension, where the upper fluid is
bounded above by a rigid lid and the lower fluid is bounded below by a flat
bottom. We use a spatial dynamics approach and formulate the steady Euler
equations as an infinite-dimensional Hamiltonian system, where an unbounded
spatial direction $x$ is considered as a time-like coordinate. In addition we
consider wave motions that are periodic in another direction $z$. By analyzing
the dispersion relation we detect several bifurcation scenarios, two of which
we study further: a type of $00(\mathrm{i}s)(\mathrm{i}\kappa_0)$ resonance and
a Hamiltonian-Hopf bifurcation. The bifurcations are investigated by performing
a center-manifold reduction, which yields a finite-dimensional Hamiltonian
system. For this finite-dimensional system we establish the existence of
periodic and homoclinic orbits, which correspond to, respectively, doubly
periodic travelling waves and oblique travelling waves with a dark or bright
solitary wave profile in the $x$-direction. The former are obtained using a
variational Lyapunov-Schmidt reduction and the latter by first applying a
normal form transformation and then studying the resulting canonical system of
equations.
