Excerpt from the Kriegstagebuch Machine Section.
	B. E  x  p  e  r  i  e  n  c  e a) Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . b) Machinery diving and refueling equipment.   1.  Mechanical installation::           Major malfunctions of the diesel engines did not occur until Failure A 1 (cylinder crack). The diesels suffered greatly when blowing the ballast tanks.  Blowing takes place at 400-440 rpm with cut in supercharger at 0.8-0.9 atm blowing pressure. The safety valves have been adjusted accordingly.  Blowing without supercharger or in reverse gear is not possible, since a blowing pressure of only 0.65 atm is achieved.  With prolonged submerged cruise the diesels cool down substantially and with the same blowing at high RPM, the seals between the cylinder head and cylinder leak very quickly.  Tightening is not possible because of the strong taper already made by the shipyard (see AI). The supercharger knocks strongly when blowing.  Installing a blower for blowing the ballast tanks is deemed necessary.           The E-motors (S.S.W. GU 343/38 - 8 276 KW) are too weak for the stocky form of the boat.  At the transition from diesel to electric motor (alarm), the boat loses speed depending on sea conditions up to 0 knots.  The backs of the panels need to be shielded from condensation better. The fresh water generator has not been put into operation since water was not supplied.  Since the delivery of fresh water, if any, will take place only within narrow limits, it is proposed to remove one fresh water generator and in its place install an electrically heated drying cabinet.  This has proven to be very necessary as 2/3 of the crew is completely soaked during the supply maneuvers. With the limited outfitting that is unsustainable because the clothes can not be dried in the required time in the E-motor and Diesel engine rooms, and the people are forced to stand their watch in wet clothes, a fact which in the colder months must lead to the first health disorders.

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	The freezer is well proven when apart from the incidents listed under A 10 and A 12. This could have been avoided if the designed normal packages were present at the location of the stored fresh meat, isolated with wax packaging, not freezing together as the fresh meat was frozen into a block. In addition to the damage to the installation caused by breaking out of the meat there was heavy cooling loss.  The room air cooling system has not yet been put into operation.
	2.  Diving installation:
	The boat proceeded on the outbound and return transit in buoyancy condition B with flooded main ballast tanks, because the testing and training time showed in the main, that the boat gets below very badly even in the slightest Sea State in buoyancy condition A.  Failure in the vent actuators has not yet occurred.  It has been found necessary to flood main ballast tank 9 immediately on "Alarm", on "Flood" to open the vents of the ballast tanks 5/6 and to wait to open ballast tanks 1/2 until the boat is 3-5 degrees down by the bow.  Expressing of the negative buoyancy tanks not before 14-16 meters, because otherwise the danger exists that the boat will emerge again.
	[several illegible sentences here]
	To blow with diesel a blowing pressure of 0.8 - 0.9 atm is used for up to 15 minutes. (See also b 1 of the Mechanical Supplement) the installation of a blower (type UD 2 - UD 5)

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	only to blow the ballast tanks and bunkers is suggested as appropriate.
	3.  Fueling installation:
	The supplying of boats with fuel and lubricating oil functioned without difficulties.  The sight glass built-in the delivery line (control room) has been proven.  It would be appropriate to install a drain in the delivery line, specifically at the outlet fuel oil meter (lowest point), so that after rinsing and blowing the hose and delivery line the last residual water in the line can be emptied from the deck.
	Delivery was made with a pump outlet pressure of 1.4 - 2.5 atm.  At this pressure, said to be the maximum pressure by the receiving boats, IXC boats achieved an hourly output of 35 m³ and VIIC boats 30 m³.  Of course the decisive factor is the number of the bunker used on the receiving boat. Adjustment of the delivery can be effected only by movement of the pump intake.  In the process of adjusting [fuel is] very often completely cut off and the pump runs dry.  According to the shipyard that should be avoided if possible.  It is therefore suggested to make the speed of the pump adjustable, and set the current normal RPM as the highest RPM.
	The oil transfer hose and gear was damaged in several cases and lost in part.
	Damaged:  2 hoses 16 meters x 90 mm, 2 hoses 16 meters x 65 mm, 1 hose 8 meters x 90 mm with protective covering, 1 hose 8 meters x 65 mm with protective covering and 1 each stop cock 90 and 65 mm.
	Lost:  7 hoses 16 meters x 90 mm, 1 hose 8 meters x 90 mm, 5 hoses 16 meters x 65 mm, 2 hoses 8 meters x 90 mm with protective covering, 1 each stop cock 90 and 65 mm, 3 coil end supports 90 mm, external thread with 45 mm end coupling, 1 end coupling 52/45 mm, 4 closure caps 90 mm, external thread with compressed air connection, 2 closure caps 90 mm with internal thread with compressed air connection, 2 compressed air connection pieces 1/2 inches external and 3/4 inch internal thread and 8 closure caps for compressed air

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	nozzles 3/4 inch inner thread.
	The damage or loss occurred during maneuvers or were due to sea conditions.  For quick repair of damaged hoses, 10 each light metal pipe pieces 90 x 100 and 65 x 300 with strain bandages  were deemed necessary.
	Overview of times, pressures and volumes of fuel oil transfer
Date Boat No. Boat type Duration of fueling Suction side Pressure side No. of bunker used With delivery rate Output fuel oil quantity Remarks - - - hours/min atm atm - m³/hour m³ - 20 Apr U-108 IXC 0/43 -0.24 +1.6 - 34.9 40 23 Apr U-98 VIIC 1/57 +0.10 +1.4 4 27.6 40 23 Apr U-333 VIIC 1/37 +0.15 +2.0 6 27.8 40 23 Apr U-564 VIIC 1/15 +0.16 +2.5 3 22.6 24 24 Apr U-571 VIIC 0/58 +0.10 +1.7 2 28.4 25 24 Apr U-582 2/09 +0.09 +2.0 3 28.2 55 0/35 -0.05 +2.2 4 32.1 17.9 0/07 -0.06 +2.2 3 32.4 3.7 25 Apr U-552 VIIC 0/26 -0.06 +2.2 2 31.3 12.9 0/04 -0.07 +2.5 1 24.4 1.5 1/12 - - - 30.1 35 27 Apr U-566 VIIC 2/32 +0.05 +2.0 4 29.3 36 55 min. interruption 0/47 +0.08 +2.3 2 20.9 17.5 29 Apr U-572 VIIC 0/30 _0.04 +2.2 3 28.5 13.2 0/16 -0.05 +1.6 1 18.5 4.3 1/33 - - - 22.6 35 29 Apr U-594 VIIC 1/14 +0.08 +2.3 3 26.5 25 12 min. interruption 0/40 +0.08 +2.0 5 31.9 22.5 29 Apr U-69 VIIC 0/20 -0.05 +1.5 2 15.2 5.9 0/15 -0.07 +1.6 1 14.1 3.6 1/15 - - - 20.4 32 29 Apr U-558 VIIC 2/14 +0.20 +2.5 - 24.1 30 50 min. interruption hose jammed                   1 May U-754 VIIC 2/25 +0.30 +3.0 6 14.4 30 2 May U-103 IXC 2/25 +0.30 +3.0 1 13.8 30 5 May U-753 VIIC 1/47 +0.20 +2.5 1 10.5 20
	The lubricating oil transfer worked, apart from the fact that only 5 boats took over lubricating oil.
	c) Experience concerning trim and weight conditions.           The boat could no longer make its final trim test (U.A.K.) after ballasting in the yard due to the ice conditions.  Only a normal trim  test in the presence U.A.K.was made in 10 meters water depth for the approximate determination of the weight conditions.   As equipping came on board: 720,700 m³ of fuel oil, 34,300 m³ lubricating oil, 877 potash cartridges, 10,470 m³ of fresh water, 3350 m³ distillate,

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	25,700 Kg. provisions and the normal outfitting gear and consumables minus 323 potash cartridges and 70 oxygen cartridges with a total weight of 1291-840 = 2132 Kg.
	Total capacity of both regulating tanks      55.920 m³ Total capacity of both trim tanks  16.269 m³ Contents after the trim test at Helgoland:                                               Regulating tanks 46.150 m³                                               Trim tanks 7.840 m³
	On 1 April the starboard negative buoyancy tanks was out of service.  With this the contents decreased to 46.150 - 7.970 - 38,180 m³.  The port negative buoyancy tank continued in service.  Sea water density was between 1.0265 = 1.027 .grams/ml.
	Total consumption up to 4 May 1942 inclusive: Fuel oil: transferred 477 m³ Own consumption 120 m³ = 597 m³ Weight increase of the boat 101.49 m³     Transfer and consumption (weight relief) Provisions 19.100   tons   Lubricating oil 6.871     "        (7,635 m³)   Potash cartridges 1.492     "        (373 units)   Fresh water 7.120     "   distilled water                     0.700     "   Total 35.285     "
	Other offset weight:
	The fuel oil bunkers:  11-41 were pumped.  20.000 m³.  Lubricating oil whose transfer was not to be expected, pumped via lubricating oil transfer piping into fuel oil bunker 4a port. 25 m³.
	Compensating weight:
	Regulating 38.180 m³   Transferred 35.283 m³   11-41 20.000 m³   Lubricating oil       25.000 m³   Total: 118.463 m³   Weight increase 101.490 m³   s.Vfg. i regulating tank 16.973 m³   Actual regulating contents On 4 May 13.705 m³
	Still to be expected delivery and own consumption of fuel oil 20 + 60 m³ = 80 m³.   Weight increase 13.6 m³.

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	Highest possible weight relief:
	Fresh water 3.000 m³   Distilled water 1.400 m³   Lubricating oil 1.000 m³   Provisions transferred 15000 m³   Provisions own consumption 1500 m³   Potash cartridges                     1.500 m³   (250 units on board) To Vfg.regulating tank 9.400 m³  + 0.105 m³ = 9.505 m³
	The filling of the regulating tanks to 46.150 m³ is at the correct limit, to ensure the flooding of the regulating tanks and the compressed air pumping with the pumping controller. The regulating tank itself is too small for the purposes of the boat.  Apart from the negative buoyancy tanks, the reserve hose container and torpedo containers in the over deck that do not always hold tight, the delivery to each boat is different.  Lubricating oil was delivered in 4 cases, delivery to returnees only on vigorous insistence.  Spare parts and consumables in such a small amount that their weight does not figure.  To create manageable weight conditions, 25 m³ of lubricating oil was pumped via lubricating oil transfer piping via a hose connection into fuel oil bunker 4a port. This oil must be discharged and cleaned. Fresh water and distilled water were reduced to a minimum quantity.   It is desirable to enlarge the regulating space around 10-15 m³ to provide better weight conditions. It is suggested to remove from the ballast keel the equivalent of the contents of a negative buoyancy tank and use the negative buoyancy tank as a spare regulating tank, until the mode of the regulating tank can be converted.  It is also proposed the lubricating oil bunker 5 be separated by a medium long bulkhead and each half of fuel oil bunker 3 i and 4 be connected. (removal of the transverse bulkhead possible without laying pipes) these bunkers are pumpable. There would still be 20 m³ lubricating oil on board, an amount that is considered sufficient from the experience of this patrol.
	The trim conditions are sufficient.

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	d) Summary of the proposed changes.   1.) Attaching through latches in the deep freezer installation.   2.) Install a blower to blow the ballast tanks as in UD 2 - UD 5.   3.) Investigate the possibility of installing stronger E-motors.   4.) Cutting of slots in the lateral plating of the upper deck.   5.) Removal of a fresh water generator and in exchange installation of a drying cabinet.   6.) Installation of a drainage valve in the lowest part of the fuel oil delivery line.   7.) Installation of a speed controller for the fuel oil delivery pump.   8.) Increase oil transfer gear by 10 light metal tubes 90 x 300 mm and 65 x 300 mm.   9.) Lighten the boat by the contents of one negative buoyancy tank to increase the z.Vfg. of the existing regulating space.   10.) Extension of the lubricating oil supply tank 9 at fuel oil bunker 3 i and 4 i.     Other suggestions:           Installing a drain line with valve from the bow compartment bilge to the bilge of Provisions Compartment 3.  Only the main drainage line is connected to this bilge.  Accumulating water (approximately 0.5 - 1.0 m³) is only pumpable with the main bilge pump. A drain pipe to Provision Compartment 3 means significant simplification.