This article is one of the references recommended by Wingnut Wings and it's very good. Here is a quote:
ln the post-war fighting between volunteer German units and Russian Bolshevik troops in the Baltic countries, both the Junkers D I and the two-seat Cl I fighters saw intensive combat service. Air support was provided by Kamp/Geschwader Sachsenberg under command of the redoubtable Ltn Gotthard Sachsenberg. On 8 September 1919, after his return to Germany, Sachsenberg wrote Junkers that he had requested and received approximately 30 Junkers aircraft, split in equal parts between the Cl I and D I. Except for a few photographs, little is known of the history of the first all-metal aircraft in combat.
Sachsenberg continued: "The Junkers aircraft have proved themselves beyond all expectation. The weather resistance of the aircraft is so great, that it was possible to allow the aircraft to stand for weeks on end in the open during the snow, rain and thaw of the March season. A tarpaulin cover over the propeller and engine sufficed to provide protection. Since neither tents nor hangars were available, no other aircraft except the Junkers would have been able to serve in Russia at that time . . . the advantage of the weather resistance, the exceptional speed and invulnerability of the aircraft outweigh the small disadvantages. ln crashes and emergency landings relatively little occurred . . . the Junkers aircraft, with improvement, will without doubt, take first rank as a combat type."