Birds foraging under water are collectively called diving birds. For example, the brown dipper, little grebe, common cormorant, tufted duck seen in rivers, ponds and lakes are classified into this category. Of course, penguins and shearwaters are typical of diving birds very familiar with us. High diving performance of the diving birds is expected to be useful for improving the performance of the current ships and developing new underwater vehicles. In this review article, the drag coefficient of the diving birds is introduced because it is one of key parameters for designing ships and underwater vehicles.