The correct answer is B) to carry cargoes such as steel products or drums. Half-height containers are used when the cargo being transported has a high density, such as steel products or drums. These containers allow for efficient stowage of high-density cargoes while optimizing the use of available space on the vessel. They are not primarily used for low-density cargoes (option A) or to double the stowage capacity of the vessel (option D). While stowage space limitations may be a factor in using half-height containers (option C), the main reason is to accommodate the specific characteristics of the cargo being transported.