Roswell in 1947 heralded perhaps the first and definitely the most public allegations of conspiracy and cover-up by the US military following press reports of a UFO crash. This incident began with the front-page story of an official press release by a Lt. Walter Haut on July 8 reporting "RAAF Captures Flying Saucer on Ranch in Roswell Region". What followed was nothing short of a mockery with the infamous retraction issued the following day which denied the flying saucer report and described the crash' as a weather balloon.
Over the years many witnesses have come forward to debunk the weather balloon explanation, some even claiming threats of death silenced them at the time. Unfortunately considerable damage had already been done with claim, counter claim and the "Hollywood" aspect that exaggerated any chance of truth for effect and sales. The Roswell incident remains as an ambiguous incident for which the US military clearly covered up something they considered too much of a national security risk for the general public to know.
We could speculate that a major concern driving the need to maintain a cover up is impact on general population if it were to become known that UFO's are in fact real, and are routinely visiting our planet. Attacking that which we do not understand is one of the less admirable characteristics of human nature therefore it cannot be dismissed as a valid cause of concern by the US government or military should UFO encounters be proved.
UFO sightings occur world wide, day or night and are not always in remote locations. There are many well-documented occasions where a UFO sighting was witnessed by many thousands of people at the same time yet for some reason the official response is always a denial accompanied by vague explanations of natural phenomena, weather balloons or atmospheric activity of some kind. The US military is doing precisely what every other nation's government and military seem to be doing with respect to debunking UFO sightings or encounters.
Another common experience with UFO encounters are the thousands of alien abductions reported during which various experiments are experienced are supposed to have occurred. Few of these encounters are pleasant and a significant number involve internal examinations of a sexual nature that are clearly terrifying and painful. Imagine if it were proved beyond doubt these encounters were routine, random and could happen to you.
Speculation is rife suggesting the US military gained a significant degree of technological advantage ranging from stealth technology, fiber-optics, high-speed computer capability and the like. If this were true it would certainly be a matter of national security to maintain secrecy, hence the complex strategies used to maintain the cover-up with respect to UFO sightings and contact.
UFO sightings are a historical fact with reports dating back thousands of years. Ancient rock paintings depicting helmeted bi-pod figures and even primitive pictures of spacecraft rising on plumes of fire are found in many places around the world. It seems ludicrous that the US military continues to maintain the position of denial given the millions of reported sightings throughout recorded history, and that continue today. Believers are routinely considered as unbalanced in some way and this forms one of the most effective means of maintaining the official cover-up. Perhaps one day all speculation will be ended with a public landing and friendly greeting from another world!