The Problem of Air Reconnaissance
Since Dönitz’s efforts to locate convoys with U-boats alone remained unrewarded, it may be wondered why no air reconnaissance was provided. Had there been no pre-war preparations for aircraft to support U-boat operations? In peace the Navy had certainly envisaged air co-operation; they regarded aircraft as vital for U-boat operations. Joint maneuvers with reconnaissance aircraft and U-boats had shown co-operation to be possible. These exercises had been carried out in the North Sea and the Baltic, areas which aircraft could reach from Germany, but air support was also planned for the Atlantic. In the winter war game of 1938/39, in which officers of the Naval Air Command participated, a daily reconnaissance had been made around Britain and Ireland; the outward course of the aircraft was over the North Sea and the Shetlands, the return route over France.
Suitable types of aircraft were expected to be ready within the near future. At the outbreak of war, however, such types were not available and it was impossible to aid the U-boat operations west of England. In 1939, discussions on Atlantic reconnaissance took place between F.O. U-boats and the officer appointed to the command of the future long-range reconnaissance unit, I. /KG. 40. The air experts believed that aircraft would be able to fly over France to the main U-boat operational area west of the Channel and back. But there was no air support, as I. /KG. 40 was not ready for operations until the summer of 1940. When the conquest of France gave us air bases on the Atlantic, the problem of support for Atlantic operations was again raised by the Naval Staff. On 8th June, 1940, the U-boat Staff Officer in the Naval Staff Operations Division wrote:
“. With the newly acquired operational bases in northwest France the possibility arises of air reconnaissance of the enemy convoy routes and disposition in the area south and southwest of Ireland and perhaps even in the remoter areas to the west and north. The task of the aircraft will be to intercept enemy convoys and other valuable ships, shadow them and, even if contact should be lost, regain it on the following morning…”
On 18th June, 1940, the Naval Staff issued the first directives for support of the U-boats by the Naval Air Force. Dönitz was asked to propose plans for direct co-operation between his Headquarters and those of the Naval Air Commander. In the same month the Luftwaffe Operations Staff were approached to discover the intentions of their Commander-in-Chief regarding air warfare at sea and air support for the Atlantic operations.
At first the only available aircraft were those of the Naval Air Force, namely Coastal Reconnaissance Gruppe 406 under Naval Group West and Coastal Reconnaissance Gruppe 506 under Naval Group North. The following entries on air co-operation appear in the War Diary of F.O. U-boats:
“… 26th July, 1940 – Conference with Naval Air Commander… West At present only four Do 18.. From 29th July some Do 17 and three Do 26 will be available and later some He 115.
14th August – From today KG. 40 (Fourth Fliegerkorps) will operate on reconnaissance in our operational area off the North Channel.
1st October – The Luftwaffe, which should reconnoitre to the northeast and southwest of the operational area, i.e. around Rockall Bank, has, despite all my endeavours, reported no forces available for this task.
15th November – I approach Naval Groups North and West with a request for reconnaissance northwest of Scotland and west of Ireland.
16th November – Both groups agree to the suggested reconnaissance and order it to be carried out today… The reconnaissance planned in the area near the North Channel can only be partly carried out in the northwest because one aircraft crashed.
9th December – Air reconnaissance by Gruppe 406 (mostly type BV 138) must be provisionally postponed for two months owing to mechanical defects in the aircraft.
14th December – A loose form of co-operation has been achieved with the following units:
- Coastal Reconnaissance Gruppe 406, Brest, which is under the tactical control of Naval Group West; their long-range BV 138 will not be employed for some two months.
- KG.40, Bordeaux. They are independent, and co-operation is due only to personal contact. Type FW 200. At present there is usually only one aircraft available daily.
- Luftflotte 5. They require previous notice for reconnaissance in a specified area. To date, only one flight made. Several requests were recently refused owing to lack of aircraft.”
Five months had passed since the capture of the Atlantic bases, but no progress had been made. In fact air reconnaissance was negligible; usually one aircraft, and never more than three, were available daily for operations, and F.O. U-boats was not able to direct these to suit his requirements.
F.O. U-Boats demands Air Reconnaissance Forces
By the late Autumn of 1940 the problem of locating targets had become urgent, and Dönitz again sent the Naval Staff a list of his requirements for air reconnaissance. His war diary for 14th December, 1940, stated:
“The war has shown that the lise of U-boat packs against convoys is right and can be very effective. However, in every case contact with a convoy was achieved only by chance. Should no convoy approach them, the boats might be at sea for days without result. They waste their time in the operational area, unable to make the most of their striking power,”
“The power to dispose the aircraft for reconnaissance must lie with the Command for which they are working. Further co-operation once a convoy is sighted, such as shadowing and the sending of homing signals by aircraft at daybreak, must be directed by the Command in charge of the convoy action. This will not interfere with tactical control by the flight commander. In other words, F.O. U-boats must determine the reconnaissance area and the number of aircraft required; he must be able to direct all forces in order to ensure an effective, unified operation…”
1./KG.40 Bordeaux subordinated to F.O. U-boats
A conference on further operational plans was held in Berlin. On 2nd January, 1941, Dönitz at the suggestion of the Commander-in-Chief, Navy, approached General JodI, Chief of the Operational Staff in the Supreme Command, stating his requirements, including the necessity for operational subordination of the air reconnaissance units. He wanted a minimum of twelve very long-range aircraft to be available always for daily simultaneous reconnaissance of the operational area. The outcome of this discussion was a decision by the Führer whereby from 7th January l./KG.40 was to be allocated and subordinated to F.O. U-boats for tactical reconnaissance. This was the only long-range unit (of FW 200) capable of penetrating as far as 20° West.
The Führer’s decision was made while Goring was away on a hunting trip, and was contrary to his wishes. On 7th February Goring had a discussion with Dönitz in France, at which he attempted to persuade the latter to agree to a cancellation of the Führer’s order. But Dönitz was adamant, for he saw no other way of solving the problem. Goring conducted the discussion in an unprofessional manner, making it clear that little support could be expected from him. Though he appeared to realise the necessity for supporting naval operations, he saw in the subordination of I./KG.40 to F.O. U-boats the beginnings of a naval air force, and his objections to this outweighed all other considerations.
Reconnaissance by 1./KG.40
On 7th January, 1941, I./KG.40 was placed under the operational control of F.O. U-boats, who commented:-”… This order marks a decisive advance in U-boat warfare. It is only the first step in this direction and in view of the few aircraft available and the various technical difficulties still to be solved, the immediate effect will not be great. However, I intend to gain the best possible results from the co-operation…”.
But these tentative hopes were not to be realized. In two of the earliest reconnaissance flights on 16th and 28th January attempts were made to lead the boats to sighted convoys, but they were fruitless, for in both cases the air reconnaissance failed to regain contact with the convoy on the second day.
The first successful contact by aircraft of I./KG.40 with British shipping was due to a U-boat. U.37, while on her way to Freetown, had on 8th February sighted a homeward-bound Gibraltar convoy (HG) off Cape St. Vincent. No FW 200 had so far appeared in this area, and a surprise bomber attack promised success. The boat was ordered to shadow the convoy, with a view to homing the aircraft on to it. On the 9th February U.37 attacked the convoy (HG 53) about 160 miles west-southwest of Cape St. Vincent, sinking two ships. She” homed” six FW 200, which attacked in the afternoon, sinking another five ships. She continued to shadow and sank a further ship on 10th February. At this time Hipper was in the vicinity of the Azores and received permission to attack the convoy, acting on further homing signals from U.37 But she only succeeded in sinking a straggler, the British S.S. Iceland, on 11th February. That evening Hipper gave up the search for HG 53, and proceeded south to intercept SL (S) 64 on the strength of German Radio Intelligence. Her attack on this convoy early on 12th February resulted in the loss of seven out of nineteen ships. These operations showed the possibilities of a combined attack by aircraft, U-boats and surface ships-the first example in naval history.
In the battle area northwest of the North Channel no change was made in the U-boat dispositions and method of attack. The aircraft available from I./KG.40 were still too few to allow the U-boats to abandon their own reconnaissance. Usually only two aircraft operated each day. Whenever a special area was to be reconnoitered by four or five aircraft, or when a special bomber operation was planned, this necessarily depleted the air reconnaissance both before and after the air operations.
Thus air reconnaissance was still only an occasional aid, and F.O. U-boats still had to place his boats “where he thought best”. This” hit or miss” policy was even less satisfactory than before, for in January, 1941, the British began to spread the convoy routes over a wider area, and to send the convoys further north. Naturally it took us some weeks to collect the data from which this change was established. Until 10th February the U-boats operated west of North Channel as far as 20° West, when they began to follow up the convoy diversions to the north. The battle area stretched in stages as far as the coast of Iceland. The longest north-south extension occurred on 27th February and again on 2nd March, when seven boats were stretched between Iceland and Rockall Bank. But the northward movement of the U-boats was not conducive to co-operation with KG.40, whose aircraft, being based at Bordeaux, could only reach the southeast corner of the area. For reasons which they did not state to F.O. U-boats, the Luftwaffe found it impossible to transfer KG.40 to Stavanger airport. From the middle of February the usual procedure was for the FW 200 to take off from Bordeaux, reconnoitre the area northwest of North Channel and then land in Stavanger, returning on a reciprocal route on the following day. This procedure-though often cancelled because of the Norwegian weather-led to a number of convoy sightings and to several large-scale operations.
Support from the Air
On 19th February an aircraft en route for Stavanger sighted a westbound convoy, OB 237, 80 miles northwest of Cape Wrath. All the boats, which were then in a bunch south of Iceland, were directed to proceed southeast at maximum speed to form a patrol line ahead of the reported convoy course. On the second day the convoy was picked up by two aircraft. Their reports were so inexact that searching on that day remained without result. Further patrol lines by the boats on the next day also failed to find the convoy and the operation was abandoned on the evening of 21st February.
Two days later an aircraft returning from Stavanger sighted another westbound convoy, OB 288, 40 miles southeast of Lousy Bank. Approaching the position given by the aircraft, U.73 was able to make temporary contact a few hours later. The aircraft which took off on the following morning had insufficient range to find the convoy, but the U-boat report of the previous day was sufficiently accurate for the boats to find it again east of their patrol line. Four boats attacked and destroyed the convoy during the night, reporting nine ships sunk, which is corroborated by the British Admiralty. In this operation, as in the simultaneous operation against OB 239, torpedo failures prevented even greater results. The latter convoy was sighted by U.552 (Lt. Topp). With two more boats, also on their first operation, Topp pursued the enemy for three days, but was himself unable to obtain results owing to the heavy sea and torpedo failures. Two ships were reported sunk and one damaged. British Admiralty records give three ships sunk and one damaged.
It was by chance that OB 290, the next Atlantic convoy to leave the North Channel, was also attacked between 25th and 27th February. The sighting was not made by aircraft, but by Lt. Prien who was proceeding north. Two returning boats without torpedoes were ordered also to maintain contact until the arrival of U.99 (Kretschmer). Prien’s shadowing reports enabled six FW 200 to carry out an effective bomber attack- another instance of U-boats leading aircraft to the target. Prien reported sinking altogether 22,000 tons. British Admiralty records give three ships totalling 15,600 tons sunk, two damaged and nine sunk by FW 200.
An extensive but unsuccessful operation began on 2nd March, when an aircraft proceeding to Stavanger sighted OB 292 just west of the North Channel. All available boats were assembled in patrol line by 3rd March, while three FW 200 searched in vain for the convoy. The three aircraft reconnoitred the area southwest of North Channel more fully than the northwestern sector, so it was assumed that the convoy had been diverted to the north, and the boats were ordered to proceed slowly northwards. On the third day of the operation an aircraft returning from Stavanger found a convoy of the same composition 150 miles north of the position reported on the first day. Presumably the weather had forced it to heave to. The boats were drawn up in a new patrol line. At dawn on 5th March they proceeded eastwards to meet the convoy, but were unsuccessful. It had passed out of the range of our aircraft, and as there was no way of finding out which direction it had taken, the operation was abandoned that evening.
Air Support Inadequate
After this unsuccessful operation, F.O. U-boats decided that for the time being no more U-boats should be sent against convoys reported by aircraft. The aircraft had hardly sufficient range to direct the U-boats to outward-bound convoys. They were able to maintain contact for one or two hours (as far as 10° West) on the day of sighting, but on the second and most important day the westbound convoys would be beyond their range. In the case of convoys on northwesterly and southwesterly courses, air contact could be made only if the ships happened to be on the direct route of the aircraft, and even then there was not enough fuel for searching, shadowing, or sending homing signals. The aircraft could not even remain long enough over the convoy to deduce its mean line of advance. No air reconnaissance could be provided for attacks on homeward bound convoys as the aircraft could not reach the northern area. Aircraft reports on convoy positions were often badly in error. A comparison of convoy positions reported by aircraft, U-boats and the Radio Intercept Service showed that the aircraft reports were sometimes as much as 70 miles in error. This was the reason for the failure of the actions against OB 287 and OB 292.
Too few aircraft had been available for all these operations. Daily reconnaissance by two aircraft-relying only on visual location-could not be effective. F.O. U-boats estimated that once the British knew of the aircraft/U-boat co-operation, their convoys would always be diverted on sighting an air shadower. With a view to keeping the air shadowers unobserved, they were ordered on 3rd March not to bomb the convoys. F.O. U-boats took this step reluctantly, being aware of the tonic effect of successful air attacks on aircrews engaged in long and wearying reconnaissance. But the large Kondors found unobserved shadowing impossible, and on 31st March general freedom of bomber attack on all targets was restored.
Steps to strengthen Air Support
The situation could only be improved by the allocation of more aircraft, which, according to the Commander-in-Chief of the Luftwaffe, would be forthcoming. Aircraft of longer range were in process of development and construction. The FW 200 must serve until these were available. During the following months additional fuel tanks were installed in the FW 200 to improve their range.
On 3rd May F.O. U-boats issued the following orders to improve the methods of determining position:
“… Aircraft will take off on the same route at intervals of one to two hours. Convoys are the objective of reconnaissance. They should be reported as quickly as possible by homing signals giving position, course and speed. Composition of the convoy should be reported later. Contact should be maintained as long as fuel permits. All subsequent aircraft will fly towards the convoy reported by the first aircraft, and will make independent, complete reconnaissance reports as already detailed. The first aircraft’s report will be checked with the others. Each aircraft must report its own navigational data, uninfluenced by any report of the preceding aircraft…”.
To check the aircraft position reports, the H/F-D/F shore stations were ordered to take bearings on the aircraft radio transmitters. Until this new procedure had been tried out, F.O. U-boats was reluctant to allow the U-boats to act on convoy reports from aircraft. The boats now moved further west, and the intended procedure could not be tested in the following months, nor were there any more combined operations west of North Channel. However, at the direction of F.O. U-boats, KG.40’s daily reconnaissance was continued in the area west of Ireland and northwest of North Channel. All information regarding enemy traffic, even if negative, was useful in deciding the boats’ operational areas.