After being a Captain or Co-Captain for ~5 years (!), I think that models of how leadership responsibilities are delegated and assigned in each brigade, will vary, based on the size of the brigade, number of people in leadership positions, their personality styles, their interest areas and skills, how much time they have, and even how your civic tech ecosystem/scene works locally (e.g. you may not spend as much time on recruitment if you have steady flow of newcomers).
No matter what, I’d strongly encourage you to have more than 1 person do the primary Captain/leadership tasks: onboarding/introducing people at meetings/hack nights, facilitating the overall hack nights (the structure/agenda of the meeting, taking notes at the meeting, deciding to and arranging any presentations, securing the space, etc), newsletters/social media/outreach/attending other ally organizations meetings or being the contact person for governments; that will quickly lead to burnout and/or stunt the growth of the brigade because one person can’t or shouldn’t do it all.
I’ve had some luck of:
individually asking a regular attendee before a meeting
or just aloud at the beginning of a meeting:
to complete a concrete, fixed-length task (take meeting notes tonight, take aside these 2 new attendees at this meeting and introduce Open Cleveland and civic hacking/open data to them) but some have politely declined when I asked them to the next time because often, their interest areas/motivation to be a part of Open Cleveland wasn’t strong enough or match up with their motivation to be a part of the brigade (e.g. to build their programming skills in a setting that would be positive to the public);
or more often than not, they didn’t have the time to commit on an ongoing basis.
I think mentioning the fixed-length portion is particularly effective initially because it prevents the attendee from thinking “what am i getting myself into (a long commitment?!)” and sometimes their small work creates instantly visible results (an agenda!) at the end of it.