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Black Sea trade would adversely affect Russian industry and throw extra strain on, the railways. The Allied naval forces would need to include heavy ships, cruisers, destroyers and submarines and perhaps an aircraft carrier, and we might be hard put to it to spare these forces, and particularly the smaller ships, from other services. Before we could operate naval forces in the Black Sea the provision of a secure base would be essential, and this is under active considera- tion with the Turks.
39. The whole Black Sea is within range of Soviet shore-based air forces, and this fact would impose an initial restriction on our naval operations until the measure of this threat had been obtained by experience.
General Conditions governing Attack on Russian Oil Supplies in the Caucasus.
40. The Soviet dependence on the Caucasian oilfields has already been emphasised. Subject to the factors stressed below there are three possible methods of interrupting or destroying these supplies. Firstly, by air attack; secondly, by naval action in the Black Sea and, lastly, by Turkish land operations from Eastern Anatolia.
41. All three of the above methods are governed by the fact that we cannot reach any of the Russian vulnerable points in the Black Sea or Caucasus unless we obtain the co-operation of Turkey or Iran, or infringe their territorial rights. The question whether these countries can be induced to depart from their neutral position is a political one.
42. On the assumption, however, that circumstances do enable us to secure Turkish or Iranian co-operation against Russia or to infringe their territorial rights, the following are the military factors affecting Allied action against Caucasian oil supplies.
Air attack.
43. The most vulnerable oil objectives in the Caucasus are the
of groups refineries at Baku, Grozni and Batum, of which the first is by far the most important. We are advised that a refinery, once effectively destroyed, could not be repaired under nine months at least. The Russians are well aware of the vulnerability of their oil installations in the Caucasus, which are defended by large numbers of fighters and anti-aircraft weapons, though the efficacy of these defences, being Russian, is no doubt not so formidable as their numbers would suggest. There must however remain, in the absence of any experience of sustained air action against this scale of defence, some element of doubt whether the requisite wholesale destruction of all the refineries could be carried out.
44. A plan for the attack of these installations is now being worked out by the Air Staff in the Middle East, and is also under examination in the Air Ministry. It is at present estimated that the destruction of the principal refineries might be achieved by sustained operations over a period of several weeks by a force of not less than three bomber squadrons. In the event of hostilities with Russia, it would be desirable to undertake these operations as soon as circum- stances permit, since delay would give the Russians an opportunity of improving their defences, possibly even by the addition of German fighters.
45. The plan involves operations at long range over difficult and mountainous country. The only squadrons now in the Middle East with the necessary range are three squadrons of Wellesleys. These are not suited for action by day against the scale of defence to be anticipated, though some of them might be used to supplement at night the activities of squadrons working by day. The operations must, therefore, in the main be undertaken by Mark IV Blenheims, for which we can provide the tropical equipment required to enable them to operate in this part of the world. Three squadrons of this type would, therefore, have to be provided in the Middle East, complete with the necessary reserves to enable them to replace wastage.
46. It is essential that the implications of such a course of action should be clearly understood. Whether the Mark IV Blenheims are used to re-equip Mark I Blenheim squadrons now in the Middle East, or to reinforce the Middle East Command, the fact remains that the necessary aircraft and equipment can only be found from home resources. If the aircraft of three complete squadrons
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