The initiation and propagation of a crack and an adiabatic shear band in three-dimensional finite coupled thermomechanical deformations of a homogeneous and isotropic thermoelastoviscoplastic rectangular 4340 steel plate containing a centrally located through-the-thickness elliptic void and deformed in simple tension are analyzed numerically by using the finite element computer code DYNA3D. Initially, the major and the minor axes of the elliptic void coincide with the centroidal axes of the plate. An element is assumed to have failed when the damage parameter defined in terms of histories of the effective plastic strain, the effective plastic strain rate, the triaxiality factor, and the temperature at its centroid equals one; an adiabatic shear band initiates at a point when the effective plastic strain there equals one, while the material point is deforming plastically and deformations of the surrounding material are inhomogeneous. It is found that the ratio R of lengths of the two principal axes of the void significantly influences when and where a crack and an adiabatic shear band initiate and which one initiates first They usually originate from a point on the surface of the elliptic void which is also on the midsurface of the plate, and they propagate faster in the thickness direction. An adiabatic shear band initiates sooner in the three-dimensional simulations than when displacements in the thickness direction are constrained to vanish. The crack tip follows a zigzag path that does not lie in one plane.