For those having trouble with 1948, here's a good strategy: at the start, line up your planes so they are both moving in a straight line, while dropping the green gas whenever you can. The other planes will folloew both your planes and run right into the gas, killing themselves, cause they are just plane crazy like that :D
Then take out the last plane by getting both your planes behind it, might take a bit of time but once you do the badge is yours. Hope this helps!
I prefer to combo the lasers/missiles to get the LASER MISSILE....which is a missile that shoots lasers. It circles around, destroying enemies before they even get onscreen! With that, you'll easily get to wave 100, by then you can afford the expensive stuff...buy damage boosters first!
 "Rings"){kind=icon}
 "Heroes of Gaia"){kind=icon}
 "Epsilon"){kind=icon}
 "Cover Orange Players Pack"){kind=icon}
 "Elements"){kind=icon}
 "Protector"){kind=icon}
 "SteamBirds"){kind=icon}
 "Onslaught2"){kind=icon}
 "Ether Cannon"){kind=icon}
 "My Pet Protector 2"){kind=icon}
 "Kongai"){kind=icon}
 "Dream World"){kind=icon}