What is the fine-grained topic of the following text: “Of these [six], two aircraft were certainly downed by enemy fire, three were probably hit by ‘friendly fire’ and it remains difficult to determine who shot down the last one,” according to the Moscow Defense Brief, which also said that absence of cooperation between the Russian army and Air force "led them to conduct completely separate campaigns." Only return the topic.
Downing of aircrafts in a military conflict and lack of cooperation between Russian army and Air Force.