Aircraft you own have a blue background, aircraft you can research have a slightly darker blue background, aircraft that aren’t available for research yet have a red background. The Russian tech tree not to be confused with the Russian techno treeĪircraft are divided into five ranks or eras, broadly chronologically but with some adjustments to account for performance in a game context, for example the German Do 217 J series heavy fighters in Rank II are derived from the Do 217 E bomber in Rank III.