The Bombing of Bremen in World War II by the British Royal Air Force (RAF) and US Eighth Air Force involved both indiscriminate "area bombing" and, as capacity improved, more targeted raids upon the city's military-industrial facilities. These included, the shipyards of Vulkan, AG Weser and Atlas Werke, the Valentin submarine pens, oil refineries and the aircraft works of Focke-Wolf. Early RAF raids on Bremen beginning in May 1940 had sought out these industrial and military targets but the efforts proved costly and, given limited navigation and target-location capabilities, impractical.