My first primary source is from the perspective of a world War one pilot fighting for Germany named Oswald Bolcke. He describes in journal like context his experiences fighting with the British pilots from his conscription on August 1st, 1914 to his last letter/journal entry on October 26. 1616, two days before he is killed in action.
What this primary source tells us is that being a WW1 fighting ace was very stressful, as Bolcke talks about how some of this comrades never returned from their missions. This source also tells us that it was customary to communicate with family through letters. One of the things I found interesting was not only that the book was published very soon after the war (1919) but also that the publisher was an American book company, who had just fought in opposition to Germany. Technology also plays a huge part in this book, as the airplane had just been invented less than 20 years earlier. Bolcke is considered one of the founding fathers of aerial combat and paved the way for many of his students with his aerial tactics, which were still applicable for the Second World War.