The development and long time behavior of slow mode shocks is studied by means of computer simulation. It is shown that a well defined shock can be generated and maintained for hundreds of ion gyroperiods. The damping length of the trailing magnetic wavetrain increases with time toward the fluid limit. A population of ions with density a significant fraction of the upstream density is observed to flow back upstream from the shock along the magnetic field. The speed of these backstreaming ions relative to the upstream flow is about twice the Alfven speed, which may be sufficient to excite the right hand resonant electromagnetic ion beam instability.