HF communication circuits, on an individual basis, may perform poorly during ionospheric disturbances associated with geomagnetic storms. This is especially true at middle and high latitudes. To achieve a greater degree of reliability, it is necessary to exploit various forms of diversity. The most powerful forms of diversity at HF must exploit multiple communication paths and frequencies. The most reliable communication with an individual entity (e.g., aircraft) will involve a star network involving several independent paths. Moreover, these (redundant) communication paths must have a wide range of communication bands at their disposal. Much of the paper deals with the process by which such diversity systems may provide acceptable communication reliability, even under adverse propagation conditions. A significant portion of the paper will deal with a particular system during a very realistic scenario. The specific system of interest is the GLOBALink™/HF system, a unique data communication network.