The Boeing 737-300 was the first member of the 737 Classic series and first flew in 1984.
The 737-300 prototype flew on February 24, 1984. Boeing created the Classic series to modernize the original 737 design with more efficient CFM56 turbofan engines, a redesigned wing, and updated systems.
The 737-300 was longer than earlier 737-100 and 737-200 models and could carry more passengers. Its engines were mounted beneath the wings, but their flattened lower shape helped provide ground clearance because the 737 has a relatively low landing gear.
The 737-400 and 737-500 followed as larger and smaller members of the same family. The 737 Classic should not be confused with the later 737 Next Generation or 737 MAX series, which introduced further aerodynamic and systems changes.