[MilCom] Strange Antenna on Presidential Support Vehicle???

[Daren3006-Milcom3006 at mailblocks.com]

Hello All,

This is slightly off topic but thought it would be of interest to the 
group. This September I was fortunate enough to be on the flightline at 
Andrews AFB for the arrival of President Bush on Air Force One. I 
noticed one of the Presidential support vehicles had an unusual black 
cylinder type "thing" on the top of it that I presume is some kind of 
antenna. Anyone have any ideas about what this is or what it is used 
for. I have a pic of it here. 
http://www.pbase.com/daren3006/image/36827125

Daren