The new offering was preceded to the menu by the Nacho Cheese taco, which has sold more than 350 million units and is considered by the Irvine company to be its most successful product launch in its 51-year history.
The run-up to the Cool Ranch debut was accompanied by a massive social media push and special events, including password-only previews for fans in New York, Dallas and Los Angeles.
Taco Bell plans to market the item with its largest campaign ever, including a 3-D commercial set to play in many movie theaters across the country.
But on Wednesday, the chain drew the ire of the Doritos Locos Tacos' most passionate devotees.
The chain had surprised aficionados earlier in the week by dubbing Wednesday as Fan Day and announcing on Facebook that the Cool Ranch product would be available to buy a day earlier than planned.
But after some customers showed up at stores to find that the tacos were nowhere to be found, they swarmed Twitter and Facebook to rail against Taco Bell.
Among the postings from disappointed diners was one who said he brought along 50 co-workers only to be rebuffed: "Epic fail."
Taco Bell posted a mea culpa on its website Wednesday, saying it was "humbled by the overwhelming response to Fan Day."
So amazing, it's a total no-brainer. The new Cool Ranch Doritos Locos Tacos, now at Taco Bell.
Cool Ranch Doritos Locos Tacos
Tobuscus?, Toby Turner, Justine Ezarik, iJustine