  In this note, we discuss some features of the Dirichlet S-brane, defined as a
Dirichlet boundary condition on a time-like embedding coordinate of open
strings. We analyze the Euclidean theory on the S-brane world-volume, and trace
its instability to the infinite fine-tuning of the initial conditions required
to produce an infinitely extended space-like defect. Using their equivalence
under T-duality with D-branes with supercritical electric field, we argue that
under generic perturbation, S-branes turn into D-brane / anti-D-branes. We
extract the imaginary part of the cylinder amplitude, and interpret its inverse
as a ``decay length'', beyond which a pair of S-branes annihilates. Finally, we
reconsider the boundary state of the Dirichlet S-brane and find that it is
either a solution of type II string theory with imaginary R-R fields, or a
solution of type II$^*$ with real fields. This leaves the non-BPS S-branes as
potentially physical solutions of type II string theory.
