So I just did some minor repainting on my gunboats so I can tell them apart when I run 4 of them together. The numbers are some spareWH40k decals I had laying around. 
Viper 1: "Bullshark". The leader of Viper Squadron. Typically flies the OS-1 variant.
Viper 2: "Lucky Draw". Bullshark's right hand woman, a genius with her ordinance tubes.
Viper 3: "Red Death". 29 confirmed kills.
Viper 4: "Void Skull". Takes particular pleasure in seeing opposing pilots spending their last moments sucking vacuum.
