241 Mr R. G. Casey, Minister to the United States, to Department of External Affairs
Cablegram 1231 WASHINGTON, 29 December 1941, 6.54 p.m.
MOST IMMEDIATE MOST SECRET
I have a copy of Churchill's telegram to Prime Minister  (sent via London) regarding unifi[ed]  command proposals in the South West Pacific. I have seen General Marshall (Chief of Staff United States Army) and General Arnold (Chief of United States Army Air Staff) on this this morning.
General Marshall is the moving spirit in this unifi[ed] command proposal with the strong backing of the President. 
Marshall tells me that he proposed Wavell as Supreme Commander with Brett as deputy to Wavell.
Marshall regards urgent achievement of unifi[ed] command as vital first step. He realises that the present plan may not be perfect but it is a plan on which he believes the several Governments and many fighting services involved ought to be able to agree. He has had to argue at considerable length with United States Navy and United States Army Air to get them into line on this plan.
I asked about relationship of Commonwealth Government and Australian fighting services to proposed Supreme Commander. He said that they were trying to puzzle out workable proposals now but that clearly some [senior] Australian officer or officers would need to be on Wavell's staff, but whether in executive or liaison capacity he could not say.
How New Zealand would fit into the proposals was not yet clear.
Marshall gave me copy of the first draft of the proposed 'letter of instructions' to the proposed Supreme Commander. This draft is still under active discussion between British and American war plan staffs and is still liable to be amended appreciably. Its form necessitates agreement on its contents and signature by representatives of Australia, Netherlands East Indies, British and United States Governments. Draft gives Supreme Commander command over all sea, land and air forces allotted by respective governments concerned in the 'South Western Pacific theatre', but debars him from transferring forces of any one Government from the territory of that Government except with that Government's consent.
Plan aims at achieving air superiority as soon as possible.
Draft requires Supreme Commander to submit recommendations to 'associated governments' on matters outside of his authority.
Supreme Commander's authority is at present proposed to be limited as under:
He may not relieve from duty Commander or Subordinate Commanders of armed forces of A D B U Governments  or alter major tactic[al] organisation of any constituent government's forces.
Each national component of a task force will operate under its commander. Supreme Commander will not interfere in direct communication between commanders of national components and their own governments. Supreme Commander will exercise his authority through the commanders of constituent forces of A D B U Governments. Supreme Commander will be directly responsible to the Government of his own country and communications to and from him will go through that Government. (Summary 'letter of instructions' ends.) Further telegram follows.