The Naval Military and Air Situation reported to the War Cabinet on the 5th October 1939:
15. There has been a marked decline in U-boat activity. This is attributed to various causes : -
(a) the changeover of submarines at the end of the first month of the war;
(b) the increased efficiency of our defensive measures, which tends to make attacks, particularly on convoys, more hazardous;
(c) the weather; and
(d) U-boats making passage to the coasts of the Americas to operate there.
16. In a broadcast on 30th September the German stated that they intended in future to regard every British merchant-man as a warship. They stated that several German submarines had been attacked by British merchant ships recently, and that, therefore, although German submarines had hitherto conformed to International Law in future they must retaliate.
German troop movements.
34. A week ago 43 German divisions were reported on the Western front. There are now at least 52 divisions, in addition to which elements of several other divisions have been reported. To what extent the increase is due to the transfer of division from Poland or from central Germany is not known. The main flow of reinforcements has been towards the sector between the Moselle and Rhine. Certain increases in the number of troops on the Dutch Belgian frontiers and on the southern half of the Rhine frontier have also been reported on. There has been no big concentration of German mechanised units in the frontier regions and it is believed that the majority of the mechanised divisions are refitting in Germany. They could, however, be quickly moved to any sector where an offensive was contemplated.
The Russian advance in Poland.
39. By 28th of September the Red Army had reached the general line: Grajewo (45 miles NW of Bialystock) – Miedzyrec (40 miles west of Brest-Litovsk) – Szczebrzeszyn (40 miles S.S.E. of Lublin) – Przemysal. Since that date no official communiqués have been issued regarding the line reached by the Red Army.
The rate of advance during the period 23rd September to 28th September was between six and 10 miles per day. This was considerably slower than the initial rate and affords indirect confirmation of a report that a very serious breakdown has occurred in the petrol supply of the Army.
The equipment of the first-line divisions of the Red Army is said to be good, but that of the reserve divisions pitiable. The cavalry and infantry are described as an undisciplined rabble, but the appearance of the armoured troops is satisfactory. In northern Poland the soldiers appear to be greatly impressed with the standard of living of the people.
Royal Air Force operations.
Reconnaissances in north-west and west Germany.
68. Day and night reconnaissance flights have been made by Blenheim aircraft over north-west Germany, mainly to establish the density of traffic on roads and railways, and to examine German air dispositions. Two aircraft which sets out on 28th September to reconnoitre traffic movements in the Osnabruck – Rheine area failed to return. On the 30th September 3 Blenheims left to reconnoitre aerodromes in north-west Germany: one of the aircraft was attacked soon after reaching enemy territory and returned with gun trouble. Another is believed to have come down in the North Sea, but the third flew black with photographs of a number of German aerodromes.
Over the French-German line, units of the Advanced Air Striking Force have made a number of routine reconnaissance flights into German territory by both day and night.
On 30th September five Battle aircraft were attacked at 22,000 feet over Saarbrucken by fifteen Messerschmidt fighters, with the result that four of the Battles were shot down and the fifth crashed on returning. The air gunner in the last named aircraft reported that he had shot down two Messerschmidt fighters in flames, and French ground observers confirmed one of these successes. Of the crews, totalling twelve, in the Battles which were shot down it has been established that eight escaped by parachute, and there is some evidence that a ninth similarly escaped.
See TNA CAB 66/2/23 for the full report.