Does it have machine guns behind the pilots?
No, the add-on and the chopper doesn't have machine guns behind pilots. You only have 2 pilots in the front seats and that's all. You can check for more details and images about this add-on for Microsoft Flight Simulator X game. Visit FlightSim forum to see the images of this helicopter.
FlightSim Forum: http://www.flightsim.com/vbfs/showthread.php?225816-New-Arrival-Virtavia-H-60-Blackhawk
Notice: All the products from Virtavia are sold through FlightSim. To get other models as well as free downloads, use the official website of Virtavia: http://virtavia.com/