Southern Rhodesia: Background Information on Auxiliary Air Letters

I recently bought this air letter sent to Francis J. Field, the famous dealer specializing in aerophilately, on 7 March 1947, because the text (most of it unfortunately scribbled over) mentioned air letters.

Here is a reconstruction of the text as far as air letters are concerned:

Dear Sirs,

I apologize for the delay in
replying to your air letter of 16. 1. 47
- it arrived whilst I was absent on holiday.

I regret to inform you FIRST;
S(outh) R(hodesia) 6d air letter form - the "new printing"
which I reported (and on which my air letter
to you last sent was written) is no longer
available and the form now on sale is that
on which this air letter is written. I think
the new printing to which I refer was
from a local order placed with printers in
Bulawoyo owing to stocks in Salisbury P.O.
being exhausted. My surmise is that
with the post-war Imperial Air Scheme
opening up in Bulawoyo with heavy drafts of
RAF, there was an unusual run of members of
the Air Force on the 6d letter forms -
hence the shortage and inability of the
S(outh) R(hodesian) government Lithographic Press at
Salisbury being out of stock necessitying
local printing at Bulawoyo.

Second 3d imprinted type of
air letter for use of members of the Forces.
A fair stock of the above was
held by the Postmaster at Raylton Bulawoyo
even sometime after the end of hostilities
and the posting back to Great Britain of
the RAF stationed in Bulawoyo during the
war period. Therefore the P. M. at Raylton
in order to get rid of his stock attached
a 3d adhesive stamp and sold the forms
for civilian use at 6d per air letter.

The shortage of 6d air letter
forms (which happened whilst I was away on
holiday) enabled the P. M. Raylton to
get rid of his surplus stock of the 3d
air letter form for the Forces (with the addition of a 3d adhesive for civilian
use)

I really missed the 'bus
and deeply regret I am therefore unable to
comply with your request for supplies of
the forms mentioned.

...