The Catalina could be fitted with ferry tanks in the cabin, four long metal cylinders mounted in a wooden cradle (combined capacity, of "about 325 Imperial gallons"), in a position directly below the centre of gravity, and as merely ferry tanks, had no self sealing protection. It was these tanks which allowed the very long endurance of over 24 hours, as the wing tanks could never hold enough for such endurance. The fuselage ferry tanks required that they be opened in flight, then a suction transfer pipe powered by an electric fuel pump was plunged through the opening and the pump started on its task, forcing the fuel "upstairs" into the wing tanks. These ferry tanks were also used by RAF Cats during the search for the Bismarck in May 1941, despite their lack of protection, such was the importance of the operation. Later Catalinas also had provision for underwing drop tanks, but these were very rarely used, and normally only for ferrying - however these would have been a lot safer than the earlier cabin tanks. To give a more detailed account of the operation of the cabin tanks, the following is extracted from the Pilot's and Flight Engineer's Notes for the Catalina I, IB, II, IV, IVA and IVB flying boats (AP-2036A, B, D, E & F -PN), Paragraph 1, Fuel and Oil Systems. "An electrically driven pump is mounted on top of the upper tank (except on Mk. IV, see para. 93) to which current is supplied via a flexible lead from a socket marked RECEPT AFT on the starboard aft face of bulkhead No. 4. The pump is fitted with a flexible suction hose terminating in a length of rigid pipe which can be inserted into any one of the (ferry fuel) tanks after unscrewing the blanking plug from the filler cap. The flexible delivery is connected by a union on the port side to an external pipe and fuel is pumped through this into the port wing tank via the drain valve."
The standard wing tanks of Catalinas held about 875 US gallons each side (725 Imperial) to give a total of 1,750 US (1,450 Imperial). In Part II of the Notes (para. 51 (ii), Management of Fuel System - Instructions for the use of auxiliary tanks) it is stated under sub-para. 51:ii(b) "During transfer the wing tank gauge should be watched, and when the required amount of fuel has been transferred the pump should be switched off concurrently with the shutting off of the drain valve. The port wing tank contents can then be equalised with the starboard tank contents by turning both main fuel cocks (43) to BOTH ON. After the pumping operations are finished, the suction pipe stop cock should be closed and care should be taken that any fuel remaining in the suction pipe is not splashed about indiscriminately. Tank caps should be replaced immediately." This last instruction is then followed by a further note of caution, stating: "It should also be remembered that a dangerous concentration of vapour may remain in the aircraft for some considerable time, therefore naked lights should be strictly avoided."
Thus operating these aircraft far out over the Atlantic in May 1941 looking for Germany's most formidable battleship (which was equipped with the most modern A/A radar-controlled armament) took a special kind of nervous courage.
David D