My husband and I have a "Dining Out" event at the end of next month and neither one us have to been to one. It's formal, but I'm not sure if I should go with a long dress or a shorter dress. Any suggestions from anyone who's been to this type of event would be very welcome.

he should be in mess dress. you should be in an evening gown.

Long. I have been to a few and, yeah long is it.

Get with the girls, just like you did in school. and check what they are wearing. Formal is Long Dress, not excessively revealing, and gloves. See someone from your NCO or Officer Wive's Club for specifics.You do not need to "Join" unless your husband says it is the thing to do.
Some assignments pretty much include joining if your husband ever expects to be promoted.
My wife hated the idea, until she found there were recipes to be shared, and the General's wife was under 5 ft also, and they saw "Eye to eye" below the crowd. When the General said, "Good things come in small packages", she was in! After that they were tight, and I was a wallflower. Never did get promoted.

If you're new to the Military Life Style, I suggest taking Army Family Team Building seminars (other branches have similary classes, but you'll be welcome in AFTB even if your sponsor isn't Army).

Here's WHAT TO WEAR from AFTB
FORMAL:
Military Personnel:
Army blue uniform/bow bow tie (mem) or neck tab (women)

If you're new to the Military Life Style, I suggest taking Army Family Team Building seminars (other branches have similary classes, but you'll be welcome in AFTB even if your sponsor isn't Army).

Here's WHAT TO WEAR from AFTB
FORMAL:
Military Personnel:
Army blue uniform/bow bow tie (mem) or neck tab (women)

My husband knows what he's supposed to wear. Going to my girlfriends has been the big help. I just needed to know how formal "formal" was.