Allegiant Air has announced it will add three new nonstop flights — to Memphis, Tennessee; Austin, Texas; and Chicago — from the Des Moines International Airport. The Des Moines Register reports the added flights are part of the carrier's largest expansion in the company's history. The new fights begin May 21, with service twice weekly to all three destinations. The Las Vegas-based carrier had earlier announced flights from Des Moines to Nashville, Tennessee, which start Feb. 13. Allegiant announced in November that it would make Des Moines its newest base, investing $50 million to bring in 66 employees — including pilots, flight attendants and fleet mechanics.