A couple of questions re the Services

"Royal Garrison Artillery ... the undermentioned officers ... are
appointed to the unit, with rank and precedence as in the Volunteer
Force ... Major Arthur Waldie Temple. (To be supernumerary.)"

What is the meaning of "supernumerary" in this context, please?

Peter Goodey...

He's in addition to the normal complement.

Don Phillipson...

Supernumerary means extra above the establishment
(thus free to be assigned to any duties, temporarily
or permanently.) Each military unit has an "establishment"
e.g. of one Lieutenant-Colonel as commanding officer,
two Majors (company commanders), two Captains
(also company commanders), 6 First and 10 Second
Lieutenants (platoon commanders) and so on. (There
are other permanent jobs e.g. adjutant, supply officer, etc.)
Supernumerary officers belong to the unit but can be
assigned anywhere.

"R.M.F.V.R.
Harvey Ryding Bennette from RNVR to be Lt, (with seny. of 24th June
1949). 1st Feb 1951."

I am guessing that "seny." is an abbreviation of "seniority" but again,
can someone please explain the meaning within this context?

Peter Goodey...

It's his position in the pecking order - he's more senior than someone in
the same rank who has a later seniority date.