More military questions!

1) Do Corpsmen/Medics travel armed usually? Does this vary based on
theatre? Does it vary by nationality? Or by military institution
(Navy/Army/Marines)?

2) When I asked if all Marines were still Riflemen, I wasn't alluding
exclusively to the marksmanship aspect. What I had in mind was to know
if all Marines took the full infantry basic training - learning weapons
employment, small unit tactics, etc. Or do the Aviators and others get
some abbreviated course? 

3) In the US forces, where the Queen is not head of state, what does it
mean to hold a commission? (It isn't from the Queen) Similarly, what
does it mean to hold a warrant? Who issues them? 

4) Do other nations have a distinction between rank and appointment the
same way Canadians do? We have Warrant Officers, Master Warrant Officers
and Chief Warrant Officers. We also have Regimental and Company
Sergeant-Majors, Base Warrant Officers, and a Canadian Forces Chief
Warrant Officer (appointments). It seems to me you can call these people
by either their actual rank ("Chief Warrant Peplinksi") or by their
title ("RSM Peplinksi"). Do other nations have this distinction? 

5) Are the Royal Marines in the UK considered a branch of the Army or
Navy or a separate service entirely? Do they fall under their own
Command or that of the Army or Navy? Do they have their own medics and
doctors?