The Dreidecker was eqipped with two Spandau 7.92 mm machine guns. Antony Fokker was the first ever person who succesfully designed a mechanism to allow machine guns to fire in between the propeller blades without touching them. This allowed the pilot to aim straight at the enemy plane in front. That was so revolutionary, that suddenly a lot of planes were shot down and more pilots killed. Allied pilots called themselfes 'Fokker-fodder'. The mechanism was copied by the Alies from a shot down triplane. From that moment, air to air combat was a lot more effective in terms of shooting down other aircraft. At some point later in the 1st WW, the life expectancy of a pilot of two was a lot less than for a foot soldier in the trenches.
That's what it looks like from the pilot's view in flight.