If there are alien crafts "visiting" earth i don't doubt we have tried and so have shot some down, if by luck or "skill".
The ones claimed shot down as follows

22/7/47 Roswell, NM 4 bodies13/2/48 Aztec, NM 12 bodies7/2/48 Mexico, South of Laredo TX 1 body1952
Spitzbergen, Norway 2 bodies14/8/52 Ely, Nevada 16 bodies10/9/50 Albuquerque, NM 3 bodies20/5/53 Kingman, Arizona 1 body19/6/53 Laredo,
Texas 4 bodies10/7/53 Johannesburg, S. Africa 5 bodies13/10/53 Dutton, Montana 4 bodies5/5/55 Brighton, England 4 bodies18/7/57
Carlsbad, NM 4 bodies12/6/62 Holloman AFB, NM 2 bodies10/11/64 Ft Riley, Kansas 9 bodies27/1066 N.W. Arizona 1 body18/7/72 Morroco 3
bodies10/11/73 N.W. Arizona 5 bodies12/5/76 Australian Outback 4 bodies22/7/77 N.W. Arizona 5 bodies5/4/77 S.W. Ohio 11 bodies17/8/77
Tobasco, Mexico 2 bodies11/88 Afghanistan 7 bodies5/89 South Africa 2 alive7/89 Siberia 9 alive
www.ufos-aliens.co.uk...
I have read each case the above link claims, some decent and some not...at all.
One which i have followed over the years,
The Kalahari Incident. Though i cannot agree
with the story due to the reason as i have gotten to know it, few loop holes. I do believe something went down but governments working together or
forced to co-orp?

n May 1989 we were threatened to submit to the wishes of the United States Government when an (blackened word) space vehicle was brought down by
the South African Air Force. As you are aware that exercise was a costly and internationally embarrassing event from which we have learnt not to be
swayed or distracted from international priorities.
_______________________________________________________________
According to new information provided by the source of the Lesotho Incident the craft of the Kalahari-Incident was shot down by squadron leader Gerald
Peter Goosen with a "Thor-2-Weapon" which was fixed at his Mirage jet. The "Thor-Weapon" was a MASER-gun built in the "Thor" factory in
Johannesburg.
_______________________________________________________________
We advise that President Mandela should not be briefed on the ROLD ------------------------------------------------------------------ TSR. operation
for obvious reasons. ----------------------------------- If local government starts asking questions it will be our duty to deny the existence of any
activity surrounding the ROLD TSR. operation. Disinformation of the highest order is advised. International knowledge or intterest which is of a
deefence or political nature on this incident could implicate South Africa with a possible war emergency and we have subsequently taken initiative to
raise the level of war alert to DEFCON 2.
www.think-aboutit.com...
Link Added**
[edit on 5/31/2008 by qonone]