Crispin served the US Military for much of his adult life and has been a soldier for so long that he has experience with just about any weapon and know how to handle any combat situation. Consequently, he was the top choice for the position of team leader for Echo Six and acts as the captain, but his actual rank is unclear. It is implied that he may have been a child soldier, but not confirmed.
His handle Dee-Ay is a play on "DA" or "Don't Ask", a contraction of the phrase "Don't ask, don't tell", which was an official US policy into force between 1993 and 2011. It prohibited the army to inquire about the sexual orientation of recruits, with in return the discretion of these last ones : don't ask, don't reveal. The writer and creative director Adam Bullied actually never hid from Capcom that Crispin was gay, and there was subtle references to it in the original scrip, but it didn't show in game because of its irrelevance. He did openly stated that he wanted him to be a strong, smart, decisive, precise, polite, funny and genuinely liked and admired soldier.