Strategic Warfare may feature destruction of BRPs by submarines of both sides. Japanese submarines - which have an initial advantage from their "Long Lance" torpedoes - determine their effectiveness by tracing distance to the eastern map edge from the most easterly Japanese naval base. American submarines grow in power throughout the game, their effectiveness being determined by tracing distance to Japan's oil supply route (from the Dutch East Indies to Japan) from the nearest US naval base. BRP losses from US submarines will be massive by 1944 but are limited to 1/4 of the value of Japan's overseas conquests each turn, but once they pass 15 BRPs per turn Japan begins to suffer from incremental "oil effects", gradually degrading her economy, submarines and surface fleet. Japan is deemed to be subject to "oil effects" in Winter 1941 from the US embargo, but these will probably be lifted once Japan achieves control of the Dutch East Indies (modern Indonesia).