The Americans took a high level of interest in the British research on the effect of incendiaries. American expertise and experiments added to the planning of fire bombing raids. Despite belief to the contrary, US aircraft also carried a carefully considered mix of high explosive and incendiary bombs. Large quantities of US-made oil-based incendiaries went into service with the 8th Bomber Command shortly before the Hamburg raid - this was preferred by the Americans to the magnesium-cased thermite bomb used by the British.