Tim McInnerny's character was originally named Captain Cartwright. Stephen Fry had the idea to change it to Darling (named after a boy at his school) and created a running gag which is frequently used throughout the series.
I have a cunning plan.
Captain Darling is supposed to have the same rank as Blackadder, but wears a uniform with red lapels and a red band on his cap, which would make him at least a major.
The production crew credits at the end are formatted to look like military personnel rolls. Each crew member is listed with a cryptic abbreviation of their job title (as if it were a military rank), a serial number, last name and first initial. For example, production designer Chris Hull is listed as "Dgr. 404371 Hull, C" and makeup designer Caroline Noble is credited as "M/U Dgr. 862641 Noble, C".