Everything just in order to

a) prevent Ukrainian GenStab from sending reinforcements to the Donbass, and

Everything just in order to

a) prevent Ukrainian GenStab from sending reinforcements to the Donbass, and

b) well, since the mass of the VKS - see: Su-30s, Su-34s, Su-35s - is entirely useless in Ukraine - there's a need to keep their crews busy.