LOUISVILLE, Ky. -- Taco Bell is hoping to put a new secret weapon to use to lure customers, in the form of Doritos.

The fast food chain is rolling out what it calls Doritos Locos Tacos at its nearly 5,600 restaurants nationwide. The unit of Yum Brands calls the tacos that use shells made out of Nacho Cheese Doritos the biggest product launch in its 50-year history. It plans to introduce a Doritos Cool Ranch taco shell this fall.

The company vows to spend up to $75 million to advertise the new tacos or about three times more than it typically spends to promote new menu rollouts.

The new tacos come as Taco Bell attempts to rebound from the bad publicity generated by a lawsuit a year ago that alleged the meat filling served at its restaurants didn't have enough beef to be called that. Taco Bell denounced the claim as false and spent millions to defend its filling and shore up its image. The suit was dropped about three months after it was filed, but the chain's sales have struggled.

Photos: Taco Bell's First Meal