Southwest Airlines has converted orders for 20 current generation Boeing 737s to the 737 Max, and will take delivery of these aircraft in 2023 and 2024.

It has also substituted 19 737-700s with the larger 737-800s, the carrier's chief financial officer Tammy Romo says at the Raymond James Global Airline Conference in New York today.

A Southwest spokesperson confirmed the fleet changes, which were disclosed in public for the first time today.

Of the 20 current generation 737s that have been converted, three are 737-800s while the remaining 17 are 737-700s. The -800s were initially scheduled to be delivered in 2014 while the -700s were to come on board in 2015.

With the conversion, Southwest will take delivery of 24 737 Max 8 aircraft in 2023, and another 24 in 2024. This is 10 aircraft more each year than it had originally planned.

In 2014, Southwest will take delivery of 33 737-800s, down from 36 previously, according to an updated fleet plan. In 2015, it will accept only 19 737-800s and no 737-700s. Previously, it had planned to take delivery of 36 737-700s and no 737-800s in 2015.

The Dallas-based carrier has made a host of changes to its fleet plan in recent years, as it continues to work towards a return on invested capital goal of 15%.

Updated Southwest fleet plan

Southwest fleet plan

Source: Southwest Airlines

Source: Cirium Dashboard