The experience of Apollo in "Resurrection Ship Pt. 2" was based on the real life experience of Ensign George Gay. Ensign Gay was shot down during an attack during Battle of Midway and observed the remainder of the battle while floating in the ocean. As with Apollo's witnessing the destruction of two cylon base ships, just as Gay had witnessed the destruction of two Japanese aircraft carriers.
Adama order "salvo fire". This is when the artillery batteries firing is timed to happen simultaneously in intervals for shock value. which concentrates the effect, much like a series of hammer blows.
Opening credits say there are 49,604 human survivors.