Are your gunners hidden by dials? If so, then you are at the right place.
Ducimus posted his solution to this probem, which I copied below.
Quote:
Originally Posted by
cgjimeneza 
the AA crew slots are mostly hidden by the three order roundels in the lower right corner...
Simple fix. Press the period/del key on the numbered keypad to hide the dials. Same as what you'd do when taking a screenshot. When done moving your crew around, press the period/del key again to unhide the dials.