To whom it may concern (Or Dear ____, if you know who precisely the letter is directed at)
I am writing to you concerning the recent dismissal of Officer Stephens from the (Name of your Explorers Outfit).
It has not been disclosed with us as to the reason for the dismissal of Officer Stephens, and as such I do not wish to offend or second-guess the judgments of yourself upon Officer Stephen.
However, it is my view that Officer Stephen is.... (great, nice, hard working, friendly, etc...)
Myself and fellow (colleagues? cadets? whatever you call yourselves) would like to vouch for the character of Officer Stephens and would like to request his reinstatement. (Then blab a little bit more about how great the Officer is)
Yours faithfully (if using whom it may concern)/sincerely (if writing to an individual you know),
[Your Name/Position]