F.d.U./B.d.U.'S War Log

16 - 31 May 1940

PG30265

	Date Position, Wind, Weather   and Sea State, Illumination, Events Time Air Pressure, Moonlight etc.
	16.5.           U 122 sailed from Kiel. 17.5.           U 122 reported that she was attacked by an enemy S/M in Route I.  Route I is therefore known to the enemy.  Our own U-boats have been ordered to cruise along a line 5 miles off the center of Route I, provided they have adequate navigational data.   18.5.           U 43 left Trondheim for the Atlantic.             U 37 is NW of Scotland, on her way out into the Atlantic.             U 122 is north of the line Shetlands-Bergen, on her way to Trondheim with supplies for the G.A.F.   19.5.           The auxiliary warship "KAMERUN" has been commissioned as U-boat repair ship.             U 122 entered Trondheim.             As there are so few Sperrbrechers, it is necessary to organize the outward escort of operational boats and U-boat trial runs very carefully.  Only one of the 2 Sperrbrechers 4 and 9 has magnetic gear, i.e. 4.  It must therefore be accepted that some boats will be escorted by the inadequate Sperrbrecher 9.  F.O.I.C. Northern Defenses has suggested abandoning this protection for U-boats until there actually has been enemy minelaying activity in the sea are to be passed, but this cannot be permitted.  While there are so few U-boats it is essential that all means should be used for their protection even when absolute safety is not guaranteed.   20.5.           U 28 has left Wilhelmshaven for the Atlantic.   21.5.           U 101 left Kiel for the Atlantic.               U 122 left Trondheim for Wilhelmshaven.         22.5.           Naval War Staff asked whether U-boats could now be operated off Narvik against enemy supplies.  The answer was in the negative.             Reasons:       1) In that area it does not get dark any more, the boats would therefore have to operate in positions remote from the disembarking places and would only score chance successes.
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	Date Position, Wind, Weather   and Sea State, Illumination, Events Time Air Pressure, Moonlight etc.
	2) It is certain that "MZ" does not function in that sea area, though there is still hope that better results may be obtained with this type of firing in the Atlantic.  Experiences with "AZ" have been very bad. 3) The attack on English shipping routes has once more become of first importance. 4) Finally, this area was not cleared of U-boats without reason and these reasons have not changed.           U 26 sailed for Trondheim with supplies for the G.A.F.             U 37 reported in radio message 0045:     "1) Erik Frisell air driven torpedo spontaneous ignition 75 seconds.  Sunk with gunfire.   2) Dunster Grange electric torpedo, "MZ" safe.  No success.  Electric torpedo "MZ" premature detonation 19 seconds.  Air driven torpedo miss.  Electric torpedo no success at 500 meters.  Gun action broken off."  In spite of the worst possible experiences during the Norway operation and in spite of the ever increasing danger of degaussing on the part of the enemy, I have not so far abandoned magnetic firing, for the following reasons:     1) Impact firing with switch setting "A" led to practically nothing but failures during October and April, partly because of bad depth-keeping, partly because of failure of the pistol itself.     2) "MZ" brought many successes in the southern and central North Sea and in the Atlantic (last February), despite a number of failures to fire and premature detonators.           Although information received made it appear more and more likely that the enemy was using degaussing, I still hoped to achieve something in open sea areas, until the "AZ" was satisfactorily improved.           A thorough examination of the pistol showed a number of faults in construction, and improvement and adaptation of various parts were begun.           Independently of this, I demanded that the English impact pistol captured in "Seal" be copied.  We were to go over to "AZ" as soon as the pistol was in order for impact firing.           Today's report from U 37 alters the situation:  of 5 torpedoes, 2 were premature detonators and 2 probably failed to fire.  If one or two of the torpedoes were affected by degaussing cannot be decided on present information.  In any case magnetic firing has become almost useless.  Boats at sea have therefore been ordered to go over to "AZ" with switch setting "A".           It is quite clear to me that I must expect a further considerable number of failures due to the known defects of the "AZ", but
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	Date Position, Wind, Weather   and Sea State, Illumination, Events Time Air Pressure, Moonlight etc.
	I have no other choice, unless I withdraw the boats altogether.  But I cannot lay the boats up now, of all times, without damaging the whole arm to an unpredictable degree.  As long as there is the chance of a small percentage of success, operations must be continued.         Work is already in progress on the adaptation of the impact firing unit.  It is hoped that by inserting an electric contact a large proportion of the "AZ" failures will be avoided.  The boats which are ready to sail will therefore be kept back until they have been fitted out with adapted pistols.  The delay of 2-4 days can be accepted if it will mean better results.   24.5.           U 122 entered Heligoland and from there Wilhelmshaven.  She took supplies to Trondheim and did not have any opportunity to attack.             U 37 reported by short signal that she had transferred her operations area to square BF SW sector.  In order to make cooperation between the boats possible, U 43 will also be sent to the sea area of Finisterre; it is not thought necessary to separate the operations areas.  The area west and northwest of Finisterre seems favorable, traffic coming from the Mediterranean and the South Atlantic meets here, danger from the air is slight as enemy air bases are so far away and therefore only carrier-borne a/c and long-range reconnaissance planes are to be expected.   25.5.           U 26 and U 101, which are west of the Orkneys and Herbrides on their outward passage, have been ordered to operate in the English Channel.  The development of the situation on land has led to this decision.  If, as is to be expected, the coast of Calais and Boulogne falls into our hands, cross-channel traffic between England and France, which so far has to a large extent plied the Dover-Calais Straits, will have to be drawn further west.  Le Havre and Cherbourg will have more and more valuable traffic.  Even the larger boats can operate in this sector of the Channel, the mining situation is favorable, water depths are adequate and the sea area is sufficiently wide for them to move away if necessary.   26.5.           U 48 left Kiel.             U 122 is proceeding to Kiel, as it appears that she can be made ready for operations more quickly there.   27.5.           U 28 reported engine damage which has caused considerable loss of lubricating oil.  This boat has had to be recalled, as otherwise there is the danger that she may not be able to manage on her remaining lubricating oil.  She will go to Trondheim for repairs.   28.5.           U 101 has been ordered to penetrate into the Channel and to make a situation report on the area Cherbourg - Le Havre - Dieppe.
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	Date Position, Wind, Weather   and Sea State, Illumination, Events Time Air Pressure, Moonlight etc.
	29.5.           Nothing to report. 30.5.           U 48 reports that she requires dockyard assistance, because of a leaking access hatch.  She has been sent to Trondheim in order to save time and avoid passage through the dangerous area.  Another instance of operational boat delayed for several days because the dockyard repair jobs have not been done with sufficient care. Such delays cannot be accepted.  Recently they have occurred with U 48, U 28 and U 29.  Owing to this a simultaneous operation of several boats in the reopening of warfare against merchant shipping in the Atlantic has been frustrated.   31.5.           Nothing to report.                                            (signed):  Dönitz                                  Rear Admiral and B.d.U.
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