The U.S. Forest Service is gearing up for a tough wildfire season by adding to its large air tanker fleet seven planes that fly faster and will drop a bigger payload of fire retardant than in the past.  The long-anticipated contracts total $158 million and include several models of aircraft, including one for a converted DC10 that's bigger than anything the Forest Service has used on a regular basis. The newer planes join the aging fleet of eight large tankers, mostly Korean War-era submarine chasers.