Nmap udp scan

["Kain, Becki (B.)" <bkain1 () ford com>]

According the docs at nmap.org, I thought this should work:

[/usr/bin] @fred: $ nmap -p U:161 bob.ford.com

Starting Nmap 4.20 ( http://insecure.org ) at 2007-04-25 20:03 GMT
WARNING: a TCP scan type was requested, but no tcp ports were specified.
Skipping this scan type.
All 0 scanned ports on bob.ford.com (10.21.5.250) are=20

Nmap finished: 1 IP address (1 host up) scanned in 0.117 seconds

I thought U: was for udp, not tcp?   Can anyone shed some light?  thanks