One of the impossibilities is the nature of the labor.  Much of the work here was done by prisoners who had skills and who hoped to escape the horrors normally reserved for them.  Our visit enlightens us on several aspects of these conditions.  I'll simply note that upon finishing a boat, one prisoner was chosen to chase the props holding the ship in its base.  This was the most dangerous job of all, since the ship and the props always jumped violently at this moment of entering the water.  The reward for the prisoner who escaped alive was freedom -- a great enticement for all.  In the time of this yard's original productivity, 550 ships were thus set to sea.  One, and only one, prisoner survived the breaking of the props.