The mechanical properties of materials and particularly the strength are greatly affected by the presence of defects; therefore, the theoretical strength ( approximately 10% of the Young's modulus) is not generally achievable for macroscopic objects. On the contrary, nanotubes, which are almost defect-free, should achieve the theoretical strength that would be reflected in superior mechanical properties. In this study, both tensile tests and buckling experiments of individual WS(2) nanotubes were carried out in a high-resolution scanning electron microscope. Tensile tests of MoS(2) nanotubes were simulated by means of a density-functional tight-binding-based molecular dynamics scheme as well. The combination of these studies provides a microscopic picture of the nature of the fracture process, giving insight to the strength and flexibility of the WS(2) nanotubes (tensile strength of approximately 16 GPa). Fracture analysis with recently proposed models indicates that the strength of such nanotubes is governed by a small number of defects. A fraction of the nanotubes attained the theoretical strength indicating absence of defects.