How about when our military itself is published on the internet?
"For mobile or shoot-and-scoot type operations, vehicular-mounted antennas are required. This is the standard 5-meter (161/2-foot) whip bent down to a horizontal position (fig M-9). In this configuration, the whip is essentially an asymmetrical dipole (with the vehicle body forming one side) located close to the Earth. A significant amount of energy is directed upward (fig M-6 for typical pattern) to be reflected back by the ionosphere in an umbrella pattern. For use, while operating on the move, the whip antenna must be tied across or parallel to the vehicle or shelter. This configuration is like an asymmetrical open-wire line, and it also directs some energy upwards although with less efficiency. There are still no skip zones, but received signal levels are weaker than with the whip tied back as shown in figure M-9."http://www.athensarc.org/fm2418m.asp
Note the direction and method of the mobile vertical tiedown in figure M9 carefully.