War Diary, U-108
Extract from War Diary of the “U-108”
Commanding Officer: Lieutenant Nitseche.
2:25 p.m. 49° 3’ N. 7° 5’ W.
7:10 p.m. 51° 55’ N. 15° 55’ W.
Dived to avoid 2 patrols.
9:15 p.m. 52° 05’ W. 15° 40’ N.
Several large steamers in sight bearing 50 . Formation echelon, course about 250° approaching U-108. Submerged, and approached steamers. Convoy comprises six large steamers which soon go on course 160 , distant about 3000 metres from U-108 and bearing from 80 to 90 deg. to starboard. They form double column and steam at high speed. A torpedo-boat towing a captive balloon is in charge of the convoy. Other escorts not seen. I observe a searchlight signal from the torpedo-boat and count on a new change of course, which does not take place. Meanwhile a look around reveals the presence of 5 large destroyers on my starboard hand, on divergent course. Their position is very difficult to determine because their hulls are cleverly covered with white paint in parts. Another sweep with the periscope reveals a destroyer approaching the U-108 from the starboard quarter. Owing to its dazzle painting in the darkening evening it is difficult to make out whether her bow or stern is towards the U-108. I must assume that the balloon has seen the submarine on the surface or else the wake of the periscope (at 3500 metres) in spite of the fact that it is getting dark. The searchlight signal from the torpedo-boat towing the balloon must have been made to give information to the patrols not previously sighted.
10:20 p.m. (?) Dived quickly to 50 metres. Boat down to 60 metres when the destroyer passed overhead, followed by the others. U-108 received 15 depth charges in groups of three in a short space of time. After a short interval the same were dropped again. (31 depth charges were counted) The boat sank rapidly on flooding the trimming tank, the drainage pump functioned at first and then failed. Boat thus brought down to 70 metres. Boat is down by the stern from 10 to 14 degrees, and can only be held at high speed; continues to sink to 93 metres depth since the main drain pumps have no suction or also trimming tanks are practically empty – a condition which cannot be determined with boat trimmed by the stern. The latter is more probable since blowing with compressed air and starting the trimming pump are without influence. Battery potential drops to 1.89 volts. As soon as speed is reduced, however the boat sinks further and the trim by the stern increases. To avoid further trim by the stern blew diving tank I and regulated the trim by rapid venting aided by speed and rudder. Trimmed by the head; no result obtained.
The boat loses trim but falls again from 65 to 80 metres. Blew diving tank 5; boat rises to 40 metres and steers without trim for about 5 minutes after corresponding blowing and flooding of diving tanks V, II and I, and then trims down by the head. Reduced speed, blew diving tank VII; the boat slowly resumed her normal trim, but soon again comes down by the stern by 40 degrees. High speed. Blow after tanks. Boat then plunges down with trim of 45 deg. by the head to about 100 metres and strikes bottom. Full speed astern. Blew diving tank VII, followed by excess trim aft.
11:00 p.m. Compresses air on all tanks, as the boat cannot be held at her depth and the compressed air had dropped to 94 cubic metres. Considerable phosphorescence. No enemy in sight. The boat is floating in a huge lake of oil. Blew down. Stood off on course west to recharge batteries and compressed air flasks. All tanks filled to normal level.
11:30 p.m. Alarm and crash dive to avoid destroyer about 800 metres distant on starboard hand on course 300 deg. The boat drops to 45 metres and after a short time the drainage pump picks up suction, so that this time the boat does not drop to excessive depth. Boat can be held well at 20 metres.
12:05 a.m. Stood off on course 180 degrees,
Came to surface. Proceeded further to westward.-recharged. In the dawn a heavy oil is found in the port side which can be seen for distance. The first three depth charges threw out the automatic devices on after battery. All order transmitting devices out of commission as well as all alarm gongs, the conning tower wheel and the trimming pump. Boat started to make water in increasing quantities in forward compartment while at 92 metres depth. Occasional crackling in the rivets. Investigation of the battery with litmus paper shows acid in the bilge water.
The explanation for the previous inexplicable behavior of the boat is:-
1) Flooding of the after torpedo-tank due to rupture of the upper pipe, breakage of glass in manometer tube. The blank flange inserted on 25.4 by ship force with the means on board does not hold; therefore excessive trim by the stern.
2) Filling of the port displacement tank, which cannot be drained; hence the great negative buoyancy and list of the boat.
During the voyage up to now in water of density I.027 the boat required 10 tons in the regulating tank. Owing to the flooding of the tanks this reserve buoyancy was reduced by about 4 plus 1.5 or 5.5 tons and over more by water leaking into the boat elsewhere. The condition became even more unfavorable with further consumption of fuel oil. The excessive weight of the boat at great depths, which will reoccur in the future on failure of the main drain pump, must neutralize the reserve buoyancy or even produce negative buoyancy. This excess weight, of such great magnitude and the resultant negative buoyancy which could not be counteracted would not have obtained had it been possible to hold the boat at 30 to 50 metres.
Source: German Admiralty records, transmitted in letter from U.S.N. Attache, Berlin, March 19,1930, A12-1, Submarines.