I played this game way too much on the family 286! It was so much fun, the controls and framerate were extremely smooth compared to most games of the time. I loved the dogfights, and launching carefully aimed bombs... at enemy cows, lol (j/k, sort of). But seriously, this game was so much fun, and genuinely hard to get up to the higher levels.
I don't remember exactly what level I got to, but I remember that the gun distance increased by 1 each level, and after a bunch of levels you could shoot the cow at the end of your runway. I shot my guns at the start of every level, and called the level that killed the cow "Cow". The level after that was "1 [Past The] Cow", then "2 Cow", "3 Cow", etc. I know I got to 2 Cow a bunch of times, so maybe 3 Cow or 4 Cow was my Personal Best. As you beat levels it became harder to pull out of a stall when hitting the top of the screen, eventually becoming impossible to escape stalls. It also increased the flying speed of the airplane, which became ridiculously fast, causing loops to be wider and wider. On the first level you could do a loop-de-loop in about 1/5 of the height of the screen, but by 2 Cow it was closer to half the screen. It got to the point where it became impossible to turn around to return to base without hitting the sky or hills -- so you needed to go on a Kamikaze style mission where you shot and bombed all the buildings as you went, before crashing into the mountainside at the end of the level. I think you had 5 lives per level, so it was insanely difficult and precise at high levels to destroy all the buildings.
I exclusively played with the AI enemy enabled, but what I really felt sad about was never having the opportunity to play "Sopwith" over a LAN with other humans! It was extremely fun dogfighting with the AI, but would have been a lot better dogfighting against humans. If this does get added to GOG, I hope it supports network play via whatever DOS emulator is used.