We ended the year with 718 Boeing 737 aircraft in our fleet, the largest Boeing fleet in the world.5050) Includes 32 Boeing MAX 737 aircraft in long-term storage as of Dec. 31, 2020. Includes 60 Boeing 737 Next Generation aircraft removed from the active fleet and remaining in long-term storage as of Dec. 31, 2020.
On March 13, 2019, the Federal Aviation Administration (FAA) issued an emergency order for all U.S. airlines to ground all Boeing 737 MAX (MAX) aircraft. On Nov. 18, 2020, the FAA issued official requirements to enable airlines to return the MAX to service. We satisfied applicable FAA requirements by modifying certain operating procedures, implementing enhanced Pilot training requirements, installing FAA-approved flight control software updates, and completing other required maintenance tasks specific to the MAX aircraft prior to returning the MAX to revenue service on March 11, 2021.
Our top priority is, and always will be, the Safety of our Employees and Customers. Our Southwest Flight Operations Leadership Team has reviewed and expressed confidence in the MAX software and training updates. Additionally, aviation regulators from countries around the world have reviewed the changes to the aircraft and the FAA’s new requirements.
At Southwest, we only operate Boeing 737 aircraft, and our Pilots are highly trained and experienced at flying the aircraft. Before the MAX was grounded, Southwest Pilots flew almost 40,000 flights on the aircraft, which represents more than 89,000 flight hours. Prior to returning the MAX to revenue service, active Southwest Pilots completed additional FAA-required flight training in one of our nine 737 MAX 8 simulators and completed additional FAA-required computer-based training covering MAX procedures. We also required active Pilots to retake our original 737 MAX 8 computer-based differences training as a refresher to complement the FAA-required training. Additionally, we conducted more than 200 readiness flights on our MAX fleet and completed the software updates and thousands of hours of work and inspections before any of our Customers once again boarded a Southwest 737 MAX 8.
See Footnotes: 5151) Includes 32 Boeing MAX 737 aircraft in long-term storage as of Dec. 31, 2020. Includes 60 Boeing 737 Next Generation aircraft removed from the active fleet and remaining in long-term storage as of Dec. 31, 2020.
After completing each of these important milestones, we were thrilled to return the MAX to revenue service on March 11, 2021. We remain confident in the MAX, and it is our growth aircraft for the future. As compared with the prior generation of 737 aircraft, the MAX provides increased range, the Boeing Sky Interior (similar to the 737-800s), improved flight deck capabilities, a quieter engine, is approximately 14% more fuel-efficient.5252) The 737 MAX 8 is approximately 14 percent more fuel-efficient than the 737-800. The MAX 7 is expected to produce comparable fuel efficiency improvement compared with the 737-700.
Southwest recently restructured our delivery schedule for MAX aircraft with The Boeing Company, including the selection of the 737 MAX 7 aircraft as the successor aircraft to its 737-700 model. Southwest added 100 firm orders for 737 MAX 7 aircraft, in addition to adding 155 MAX options through 2031. This agreement underscore’s Southwest’s commitment to continued modernization of our fleet with more fuel-efficient and climate-friendly aircraft.