Many commercial aircraft are designed so that fuselage skins can elastically buckle below limit load and continue to operate safely and efficiently (Fig. 1). This design regime makes for a very lightweight semi-monocoque structure compared to a non-buckling design. Therefore, predicting the local buckling, post-buckling behavior, and failures are critical to design and optimization of this kind of structure. The local panels buckle in a combination of compression and shear. Excess compression is redistributed to surrounding axial members (frames and stringers) and shear is continued to be carried by the buckled panels via tension parallel to the buckle waves. The compression redistribution and diagonal tension put special strength considerations on all involved structural components. This post-buckling behavior and the analysis method are both called intermediate diagonal tension (IDT).