In ufology, conspiracy theory, science fiction, and comic book stories, claims or stories have circulated linking UFOs to Nazi Germany. The German UFO theories describe supposedly successful attempts to develop advanced aircraft or spacecraft prior to and during World War II, further asserting the post-war survival of these craft in secret underground bases in Antarctica, South America, or the United States, along with their creators. Early UFOs as possible Nazi technology During the Second World War, unusual sightings in the skies above Europe were often interpreted as novel Nazi technology. In the first years of the Cold War, Western nations speculated that unusual sightings might stem from Soviet deployment of captured or reverse-engineered Nazi technology. Foo fighters In World War II, the so-called "foo fighters", a variety of unusual and anomalous aerial phenomena, were witnessed by both Axis and Allied personnel. While some foo fighter reports were dismissed as the misperceptions of troops in the heat of combat, others were taken seriously, and leading scientists such as Luis Alvarez began to investigate them. In at least some cases, Allied intelligence and commanders suspected that foo fighters reported in the European theater represented advanced German aircraft or weapons, particularly given that Germans had already developed such technological innovations as V-1 and V-2 rockets and the first operational jet-powered Me 262 fighter planes. A minority of foo fighters seemed to have inflicted damage to allied aircraft. Ghost rockets Ghost rockets were rocket- or missile-shaped unidentified flying objects sighted in 1946, mostly in Sweden and nearby countries like Finland. The first reports of ghost rockets were made on February 26, 1946, by Finnish observers. About 2,000 sightings were logged between May and December 1946, with peaks on 9 and 11 August 1946. Two hundred sightings were verified with radar returns, and authorities recovered physical fragments which were attributed to ghost rockets. Investigations concluded that many ghost rocket sightings were probably caused by meteors. For example, the peaks of the sightings, on 9 and 11 August 1946, also fall within the peak of the annual Perseid meteor shower. However, most ghost rocket sightings did not occur during meteor shower activity, and furthermore displayed characteristics inconsistent with meteors, such as reported maneuverability. Debate continues as to the origins of the unidentified ghost rockets. In 1946, however, it was thought likely that they originated from the former German rocket facility at Peenemünde, and were long-range tests