What was the first Union unit to attack Fort Wagner in July of 1863?

Note: Most people think it was the 54th Massachusetts thanks to the movie Glory, but their failed attack on July 18, 1863 was actually the second major assault on Fort Wagner, the first of which happened a week earlier.

Forces led by Brig. General Quincy Gillmore of Strong's Brigade. That's the best I can do.

That is good enough. I read my answer wrong when I wrote the question and was thinking that only one unit made the attack when really it was multiple units within Strong's Brigade. The unit I was reading about was the 7th Connecticut who advanced the furthest, but then were repulsed.

Ah, here is a good follow up to the question - How many Confederate soldiers were killed in the first Battle of Fort Wagner.

12

Yep. Nice job. 12 lives seems small when compared to other battles but still would have been a terrible loss for the families involved.