COLORADO SPRINGS, Colorado (AP) – Air Force air tankers fighting wildfires across the nation were grounded as investigators looked into what caused the deadly crash of a military cargo plane fighting a South Dakota blaze over the weekend.

The decision by the military to put seven C-130s on an indefinite "operational hold" has removed critical firefighting aircraft from the skies during one of the busiest and most destructive wildfire seasons ever to hit the West.

That left 14 federally contracted heavy tankers in use until investigators gain a better understanding of what caused the crash.