Surplus multi-engine bombers, such as this B-17 Flying Fortress of World War II fame, were converted and used to drop retardants over forested areas being hit by fire. The normal drop speed of the airplane was about 120 MPH. One pilot exceeded the danger line and dove his B-25 down through a hole in the smoke to make a drop. His speed was around 365 MPH. The airplane came apart when he dropped his retardant. One of the largest of the air tanker operators flew fire missions at that time and he stated that they lost seven converted B-25s in one year - a very dangerous occupation.

The early airplanes dropped water, then switched to borate, a chemical fire retardant. Borate was found to be a strong soil sterilant, effective on fires but detrimental to forests. Eventually borate was replaced with compounds built around fertilizer combinations that promoted forest growth after the fire had passed.

The Forest Service overseer of tanker aviation, Charlotte Larson, is quoted as saying, "The good ones (Tanker Pilots) are really good at being idle, just being calm and collected while they're waiting and waiting and waiting. They don't get frustrated. They don't lose tempers. And when the bell goes off, they get the shot of adrenaline and they're ready to go to work right now."