318 Lord Caldecote, U.K. Secretary of State for Dominion Affairs, to Mr R. G. Menzies, Prime Minister
Cablegram 173 LONDON, 31 May 1940, 1 a.m.
MOST SECRET AND PERSONAL
The High Commissioner of the Commonwealth has communicated to me your telegram to him, No. 53.  The following are replies to your various questions, so far as they are available- (1) The B.E.F. in France was composed of:-
(a) 10 Infantry Divisions, 1 Armoured Division, 3 untrained and partially equipped Divisions which were sent out to provide labour.
(b) Of the above, one Infantry Division and the bulk of the Armoured Division are South of the River Somme. The remainder are in the Northern group of armies.
(2) So far as is known, the Belgians had until recently 22 Divisions fighting: 18 Infantry; 2 Cavalry; 2 Chasseurs Ardennais.
(3) In deference to the wishes of the French, we are precluded from disclosing the number of their Divisions in France.
(4) There is nothing to add at present to paragraph 3 of my telegram Circular Z.77. 
(5) No troop carrying vessels have been sunk other than those reported in D.W. telegrams.
(6) The necessity for such an attack, if it could have been made in time, was apparent. The reasons why it was not made were probably- (a) The shock to the French High Command caused by the unexpected rapidity and completeness of the German breakthrough;
(b) The time required for the re-disposition of available French reserves;
(c) The action of the German Air Force;
(d) The speed of movement of German tank formations;
(e) Losses which reduced the reserves, and insufficient tanks.
(7) The apparent ability of the German tanks to go straight through can be explained as follows:-
The German initial attack was made by a very large number of tanks heavily supported by dive bombers: they were prepared to accept very heavy casualties to effect the break-through. The only method of stopping an attack of this nature is a continuous and complete tank obstacle held by determined troops: in the initial stages of the German attack on the Ninth French Army, neither of these factors was present. Some of the Meuse bridges were left undestroyed and the French troops in this sector had not all taken up their positions on the Meuse when the Germans arrived; the French troops here were not so well trained as in other sectors and the value of the Meuse as an obstacle was over-estimated.
Having broken through the French main line of defence, the German Armoured Divisions found themselves in country favourable for their employment with no prepared positions and no continuous obstacles; the speed of their advance made it impossible for the French to stabilize on a River line. Moreover, such opposition as could be hastily organized was quickly overcome by a slow tank attack supported by dive bombers and motor-borne Infantry.
It must, however, be emphasized that if the factors of a continuous obstacle and determined troops are present, there is no reason to assume that German tanks cannot be stopped. The British and French anti-tank guns have shown themselves capable of penetrating the armour of any German tank which has yet been used.
The following factors also contributed to the German success:-
(a) A general under-estimation by the French of the tank material at the disposal of the German Army.
(b) A River is no longer an obstacle unless defended along its entire length. The Germans have paid great attention to bridging with armoured formations.
(c) The Germans reinforcing success by rapid transfer of additional armoured formations to point of break-through. The flexibility of the armoured formations and the high standard of trail-ling of their personnel is noteworthy.
(d) German armoured formations were supplied by air, and, where necessary, they lived and supplied themselves from the country.
(e) The French probably never expected a tank attack here and the French defences were not in sufficient depth.
(8) German concentrations opposite Switzerland remain materially unchanged, though the tension in Switzerland is believed to have lessened. This and the Italian threat are containing comparatively few French Divisions.
(9) The French Air Force, both fighters and bombers, has been very fully engaged in operations and is believed to have had substantial success. French losses from all causes rather over 500 aircraft; those inflicted on the enemy probably greater but not yet known to us in detail. According to information received from the French authorities under strictest secrecy, the French factories produced 330 operational and 98 training aircraft during April. 90 operational and 41 training aircraft were obtained abroad. No attacks likely to cause extensive dislocation have yet been made on aircraft factories.
(10) The report that Allied casualties have been heavier where American aircraft employed is quite untrue, and bears the mark of enemy propaganda. Hudson aircraft are the only American type yet in operational use by the R.A.F. Their reliability has made them invaluable for their primary task of long distance reconnaissance, particularly over the sea. They are adequately armed and have not suffered disproportionate losses even on dangerous missions.
American bombers are only now coming into service with the French Air Force, and no details as to their performance in battle can yet be made available to us or to anyone else. American Curtiss fighters with the French proved definitely superior in manoeuvrability to Messerschmitts 109 and were very successful in the early months of the war. This seems to have continued in recent weeks, though we do not as yet have details.
(11) The matter is the subject of conflicting views on the part of the various Departments but the least favourable view is as follows-Home production just under 4,000,000 tons a year, imports 2 1/2 million tons a year, mobile about 8,000,000 tons, leaving an approximate deficiency of just over 1 1/2 million tons a year.
Stocks 1st May estimated at 2 3/4 million tons. If stocks were reduced to 1,000,000 tons, it is believed that internal distribution mechanism would break down, as happened in the last war. On this basis stocks would be sufficient to make good the deficiency for about one year. But it is thought that figures for consumption do not include sufficient margin for operational expenditure on the present scale. About 70 per cent of German synthetic oil production plant is situated in RUHR district and these installations have been included in the list of bombing targets. The area is, however, heavily defended and the possible scale of attack must be dictated by the air situation from day to day.