My favourite space marine chapter (well the old Mentor Legion, not so much the newer Mentors version).
Very cool story and background. They essentially act as our modern Delta Force ---- small training teams and a test bed for the development of tactics/equipment/weaponry.
Mysterious "who knows" chapter base, and their chapter master has the ultimate say in whether new technology is accepted into Imperium use (or perhaps just space marine use?). Had personally met with the Emperor or some such as well.
Back in
RT days they had a very cool targeting web system for use with their boltguns. Essentially each additional boltgun hit would boost the strength of the original shot and add a -1 save modifier. So if a squad of five guys shot at a tank, and say...four of the guys hit - the resulting attack would have been Strength 7 with a -4 save modifier etc.
LINK:
http://documents.tips/documents/white-dwarf-98.html
Starts on page 26 (the original fluff/icons/heraldry)