Fog Investigation and Dispersal Operation (FIDO) (which was sometimes referred to as "Fog Intense Dispersal Operation" or "Fog, Intense Dispersal Of") was a system used for dispersing fog and pea soup fog (dense smog) from an airfield so that aircraft could land safely. The device was developed by Arthur Hartley for British RAF bomber stations, allowing the landing of aircraft returning from raids over Germany in poor visibility by burning fuel in rows on either side of the runway.