A hat or cap is not required with dinner dress jacket uniforms, but may be worn.
From the en.wikipedia.org
Adventure cruise specialists, on the other hand, generally do not have dinner dress codes.
From the usatoday.com
The one dinner dress I own that never fails to elicit compliments from women and men alike is a Versace.
From the time.com
There are three styles of this uniform-dinner dress, dinner dress jacket, and tropical dinner dress.
From the en.wikipedia.org
The ambience is low-key and dinner dress is casual.
From the orlandosentinel.com
Additionally, officers and chief petty officers wear an evening shirt and black bow tie with dinner dress blue.
From the en.wikipedia.org
After some prying, Ms. Bash confessed that she, too, purchased her dinner dress from Nieman Marcus, but did so with some trepidation.
From the washingtontimes.com
It is almost identical to the dinner dress blue jacket, except a wing collar shirt, white waistcoat, and white tie are worn.
From the en.wikipedia.org
The formal uniform was not unlike U.S. or UK dinner-dress uniforms, cut like a civilian tailcoat without the tails, and worn with white or black bowtie and waistcoat.