In World War I, attacks on balloons were dangerous because machine guns and anti-aircraft guns formed a protective circle beneath the balloons. Therefore, pilots dove at a steep angle when they attacked. They did not attack horizontally.
This movie is an adaptation of the play "Journey's End" by R.C. Sherriff, written just after World War I. The setting is transplanted from the trenches to an airfield, but most of the characters and some incidents are almost unchanged.
At this point in his career Peter Firth was often likened to the decade-older Malcolm McDowell, especially when he appeared in Equus (1977).
The scene with the balloon observer jumping out with a parachute is re-used footage from The Blue Max (1966).
The red German biplane is a Finnish "Valmet Viima". It first flew in 1935.