A day after a systemwide technical outage, Southwest Airlines canceled 56 flights out of Baltimore-Washington International Thurgood Marshall Airport on Thursday, and 117 others were delayed.

One of the largest network disruptions in the Dallas-based airline's history led to more than 1,000 canceled flights over two days as the company spent Thursday trying to reboot its operations.

Its computer systems were back online early Thursday after about a 12-hour outage, company executives said. But with thousands of customers and their bags as well as flight crews stranded overnight across the country, much of the day was spent trying to put the pieces of its network back together.

Southwest said it canceled nearly 700 of a total 3,900 flights Wednesday and about 450 more through Thursday afternoon. Hundreds more flights were delayed.

“First of all, I want to apologize to all of our customers. This is not the kind of service that we're famous for at Southwest Airlines. This is all on us,” CEO Gary Kelly said in a Thursday morning interview with CNBC. “The operation just needs some time today to catch up. So it will be another tough day today, but not nearly as bad as yesterday.”

Chief Operating Officer Mike Van de Ven attributed the technical outage — which knocked Southwest's website and many other customer-facing parts of Southwest's operations offline, including passenger check-in, boarding passes and ticket booking — to a failed network router. A backup system also failed, extending the outage.

The Baltimore Sun contributed to this article.