intricate rules were streamlined somewhat in A World At War. Escort Carriers & Other Units US Escort carriers (CVE) - generic factors, which do not carry separate naval air squadrons - also appear in the game. They are too slow to take part in naval interceptions, but can be used to provide ground support for attacks (carrier-based air may not intercept enemy Defensive Air Support), or take part in anti-submarine warfare. Japan may build Island Fortresses (1 per turn), which receive an extra +1 DM if subjected to invasion. The US player receives six single-factor US Marine Divisions, added gradually to the US forcepool throughout the game, which give a countervailing DM benefit in seaborne invasions, but which must be used to take any losses resulting from such combat. The US player also receives Artificial Harbours to increase his naval basing capacity in 1944 and 1945. Strategic Warfare 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). Submarines may also operate on the map, and may attack damaged surface ships as they leave combat. Each side may also send surface factors to sea as raiders. The USA may also raid the Japanese oil route, which may also be bombed by Army Air Factors. The USA may also build strategic bombers. These are more effective than in Europe, as Japanese cities were built from wood, but will not be usable until the final turns of the game - although permissible bombing range increases throughout the game, in practice the USA needs to