The defenses menu allows you to raise and lower shields for this ship.  The
ACTIVE DEFENSE SYSTEM button is a drop-down menu which displays any shield
systems which have been installed upon this ship.  You can lower all defense
systems by selecting the NONE menu item that also appears on that list.  To
raise a defense system, simply click on the ACTIVE DEFENSE SYSTEM button and
then select the name of the shield system you wish to activate.

If your ship is already protected by a shield system, but you want to raise a
different one (such as activating your cloaking device but you are currently
protected with deflector shields) then simply select the name of the new shield
you wish to raise.  During the next turn processing, the first system will be
shut down, and immediately after the new system will be activated.
