to ball lightning are responsible for "the majority, if not all" of otherwise inexplicable sightings, especially reports of black triangle UFOs. On December 1, 2009, the Ministry of Defence quietly closed down its UFO investigations unit. The unit's hotline and email address were suspended by the MoD on that date. The MoD said there was no value in continuing to receive and investigate sightings in a release, stating that "in over fifty years, no UFO report has revealed any evidence of a potential threat to the United Kingdom. The MoD has no specific capability for identifying the nature of such sightings. There is no Defence benefit in such investigation and it would be an inappropriate use of defence resources. Furthermore, responding to reported UFO sightings diverts MoD resources from tasks that are relevant to Defence." The Guardian reported that the MoD claimed the closure would save the Ministry around £50,000 a year. The MoD said it would continue to release UFO files to the public through The National Archives. UFO reports, Parliamentary questions, and letters from members of the public were released on August 5, 2010, to the UK National Archives. "In one letter included in the files, a man alleges Churchill ordered a coverup of a WW II-era UFO encounter involving the Royal Air Force". Studies Critics argue that all UFO evidence is anecdotal and can be explained as prosaic natural phenomena. Defenders of UFO research counter that knowledge of observational data, other than what is reported in the popular media, is limited in the scientific community and further study is needed. Studies have established that the majority of UFO observations are misidentified conventional objects or natural phenomena—most commonly aircraft, balloons including sky lanterns, satellites, and astronomical objects such as meteors, bright stars and planets. A small percentage are hoaxes. Fewer than 10% of reported sightings remain unexplained after proper investigation and therefore can be classified as unidentified in the strictest sense. According to Steven Novella, proponents of the extraterrestrial hypothesis (ETH) suggest these unexplained reports are of alien spacecraft, however the null hypothesis cannot be excluded; that these reports are simply other more prosaic phenomena that cannot be identified due to lack of complete information or due to the necessary subjectivity of the reports. Novella says that instead of accepting the null hypothesis, UFO enthusiasts tend to engage in special pleading by offering outlandish, untested explanations for the