U1 Design

U1 was a design by the Krupp engineer d'Equeville for a coastal u-boat, based on the design of the export u-boats for Russia: Karp, Karas and Kambala (236t). However this was an improved design compared to the export u-boats. For example it had trim cells, while in the export design for Russia, weights had to be moved by the crew inside the u-boat to bring the trim in balance. Other improvements were a newly designed forecastle to improve seagoing capabilities, a 10cm larger diameter of the pressure hull, to some extent a different internal arrangement of the equipment, stronger ballast keel etc. The torpedo tube on the export u-boats pointed 5° downwards, not so in the German U1 where the tube was installed horizontally.

5° downwards directed torpedo tube for Russian export boats vs. U1 torpedo tube installed horizontally.

Hull

The pressure hull was made of 12mm steel sheets. It had been manufactured in several parts and was then assembled by connecting them with cast steel rings that served as transverse frames at the same time and reinforced the pressure hull. That saved the pressure hull from being squeezed already in a few meters depth. D'Equeville had used a wrong formula for the compressive strength of the pressure hull that resulted in a far too high value, and initially it was planned to manufacture the pressure hull without transverse frames.

Rings to connect each pressure hull section, that prevented the pressure hull to collapse already in a few meters depth.

The maximal save operational depth was 30 meters. This was also the test depth. The outer hull consisted of 3,5-4mm torpedo boat sheet metal, galvanized from in- and outside. The transverse frames of the outer hull were placed 50 cm apart from each other. The deck was covered with black linoleum.

Planes and Rudders

The diving planes on U1 had to be operated by wheels with pure man power, except the rudder, there were no electric motors for the diving planes, what made the maneuvring at periscope depth, in rough seas, very exhausting for the plane operators and of course this limited its operational time at periscope depth and reliability to keep this depth stable. What can also be mentioned as a design flaw is the fact that the aft planes were far in front of the screws and not behind (so that the aft planes weren't in the propulsion jet of the screws), what would have been very beneficial for maneuverability.

The new most efficient plane configuration vs. the obsolete, less efficient plane configuration

This design flaw must have been (according to plans) inherent up to U 37. U 43-44 had this plane configuration as well (according to plans).

Periscopes

The periscopes installed in the tower were both 4m in length and could be raised to 3m. Their diameter of 122mm was more slender than the standard diameter of 150mm that was used on all later designs, but they were never adapted to include the tapered heads featured on the 150mm scopes, when the upper end of the large scopes shrank to 80mm just before the war and eventually to just 40mm diameter during the war.

This image shows the diameter differences in the U 1's 122mm periscope and the 80mm, 60mm and 40mm tapered heads featured on the later periscopes.

This U 1's periscope was therefore easier to spot, as much due to the bigger wake and sea spray it caused on the surface as to the greater diameter, compared to the much smaller diameter of the upper part of the later periscopes.

Here is the wake comparison at a higher speed of the 122mm periscope of U 1 and a 150mm periscope tapered to 40mm of a 150mm periscope.

The periscopes of U 1 had a fixed field of view with a magnification of 1.25x. Note: there was no 1x setting (except in one case). All other German periscopes after U 1, had 1.5x as the lowest magnification. The reason was simple, when you look through a pipe like a periscope that limits your field of view, targets appear to be smaller or further away than they appear when seen with your eyes. This led to the problem that an observer typically overestimated the distance to the target. At 1.5x magnification, the target seemed to be approximately as big as you would observe it just with your eyes.

Unique to U 1 was a third very short periscope fitted in the front deck hatch. It wasn't retractable and had a magnification of 1x. Apparently it wasn't very useful, but as the periscopes were the only means by which a submerged u-boat could observe the situation above the water, the rule of thumb at that time was to install as many periscopes as possible to give it highest possible redundancy.

So some of the u-boats (especially the bigger ones like U-Deutschland) got a third periscope that was installed right in front of the tower. It was the so-called "control room periscope" and mostly must have been of the same type and length as the attack periscope. However, because the control room periscope wasn't installed in the tower it could have been raised only barely above the tower. So this was really just a backup periscope for the case all other periscopes were lost.

Very short periscope installed in the front deck hatch, unique to U 1. Unique because it surely wasn't of any practical use so the idea was dropped for the future designs.

Tower

The U 1's conning tower was another major design flaw, as it was too small and too low to be suitable in rough seas. It gave no cover from the high waves at all, for the crew on it. The German navy however demanded a higher tower otherwise it would have got even smaller, like on the 3 mentioned export subs for Russia. But it surely gave U 1 a greater submerged top speed and range due its naturally lower resistance, compared to the later designs with bigger towers.

A small footbridge with some railings could be mounted on the tower and were spanned with canvas but that didn’t gave much protection from the rough sea either. When the sea became rough the outlooks had to retreat into the tower below, which crippled their view, since the tower had only very small windows and were additionally affected by the sea spray. This wasn't acceptable in a war. The tower was made of 4 cm thick cast nickel steel.

A provisional lookout nest, poorly protected with canvas spanned around railings, which could have been build up and had to be removed again before diving.

Construction of U 2-4 started before enough experiences could be made with U 1 so this type of tower remained till U 4. Except U 1, their towers got later upgraded though, with metal entrenchment, which was common for all later more matured designs(see U 31 article).

Propulsion System

The kerosene( Brit: paraffin/paraffin wax. Ger: Petroleum. ) engines of U 1 were not capable of different RPM 's (which was true for all kerosene engines used on u-boats). They ran full speed all the time, making speed variation impossible, resp. they had an only narrow RPM regulation range. To solve this problem U 1 was equipped with propeller blades able to adjust the pitch angle. However, they were given up in later designs due to their poor efficiency of only 50%. In the idle state they still used up 65 HP and so on later designs another method was used that relied on complicated kerosene-electric propulsion, the so-called 3-engine gear. U2-12 got this 3-engine gear type of propulsion. U 16 got a 2-engine gear propulsion and U 13-15 had no kerosene-electric propulsion anymore, this meant that different speed settings were only possible with e-engines. The kerosene engines were not reversible.

U 1 propeller blades with adjustable pitch. Adjustable both forwards and backwards.

The imperial German navy categorically renounced the use of gasoline because of the fire and explosion risk that had caused many deadly accidents in other countries in the past. The flammable gasoline wasn't even used for the kerosene engine ignition, another system was used in which electrically heated air was drawn through the cylinder. After 3-5 minutes of preheating, the cylinders were hot enough to ignite the gaseous petroleum. Of course, the drawback to this design was that if the batteries were totally exhausted, ignition of the engines would have been impossible on the sea.

One other big disadvantage of the kerosene engines were the thick white smoke they emitted that was visble quite far and in addition the retractable exhaust pipes were quite high on some boats. Another problem was the remnants of the unburned fuel that were thrown out from the pistons into the exhaust pipe and when enough condensed there it got ignited by some sparks producing a loud bang and blowing out a fire ball that was of course especially in the night a dead giveaway. Due to this reasons the fleet command considered the kerosene driven boats as unsuitable for the war but they were used anyway.

To easy this problems it became a custom to raise the exhaust masts only a little bit above the deck and rest it on a square timber.

Batteries

The battery installation of U 1 consisted of 396 peat cells whose low capacity required them to be organized in 6 parallel arrays each with 66 batteries wired in series. U 1 was cramped with battery cells, they were installed atop each other, in the crew compartments, under the floor and even in the control room. Since they were installed up so high atop each other, the center of gravity got to high and had to be counterballanced with a 23 tons heavy lead keel.The battery voltage was 130V, delivering 3660 Ah over a 3.5 hour discharge. Since this was one of the first u-boat battery types they were pretty flawy. They could develop quite some heat and high voltage discharged wasn't possible without damaging the batteries. Another flaw of this battery shortened its life span. Furthermore during recharging they emitted sulfur into the boat. It is therefore not surprising that on the photos you can see the crew on free watch, sitting on the deck :-)

I saw some indications that the U 1 batteries might have got replaced later with better types but I am not sure yet. Usually all of the boats received many upgrades and modifications during their service life so anything is possible. From some indications I figure that the batteries were at least later sealed air tight away from the crew compartments and it seems U 1 was equipped with a ventilation system that blow the toxic battery emissions during recharge directly outside.

Rescue Installations

U 1 possessed one telephone buoy with a 80m cable that could be released from inside which would have enabled the crew to communicate with rescue forces on the surface. It contained connectors for oxygen and telephone cables that could be plugged in from outside by divers. The main bilge pump could pump 60 m³/h against 60 m water pressure.

The telephone buoy was located in the wave-breaker in front of the tower.

Armament

The armament of U 1 consisted merely of torpedos and only one 45cm torpedo tube plus two magazines, making a total of 3 torpedos.

The torpedo type used on U 1 was the C/03 torpedo. This type wasn't suited for angle shots, it had a length of 5,15m, a calibre of 45cm, a range of 3000m by 26kn speed and a 147,5 kg warhead of gun-cotton. The impact fuse ignited at an impact angle of +-30° to a perfect 90° impact angle to the surface it hit. The torpedo trailed a bubble wake behind it and could be spotted early. Given this and the fact that the target just needed to turn away only that much that the impact angle deviated more than 30° from a perfect 90° impact angle, where it would hit the target without exploding and the course instability of this torpedo of up to 2°, the optimum attack range was a short 300m. This optimal range never changed throughout the war for any of the u-boats what of course doesn't mean that they have never shot from further away, infact a lot of times they shot from much further away.

Navigational Means

The navigational reliability left some room for improvements. U 1 possessed only one magnetic compass mounted in the tower. The tower was made of nickel steel and thus nonmagnetic. So that was the only choice where the magnetic compass could be installed and worked only when the electrical installation wasn't used. The chronometer was strongly exposed to the electrical and magnetic effects of the boat and proportionally to that unreliable. Depth under the keel could only be measured with a hand lids device, which could be used submerged as well. A hand lids sounder was basically a weight on a rope that was let down from a winch and stopped automatically when it hits the ground. To use it the boat had to stop or move very slow. The speed determination with the kerosene engine propulsion was very uncertain. Later U 1 got upgraded with a gyro compass, located in the tower but this early single gyro compasses became useless in rough sea due to all the wild motions of the boat.

Habitation Installations and Live Conditions on Board

There was a toilet available in the torpedo room and it seems the galley was located on the opposite side of. The officers already had their own rooms and bunks but all the crew traffic lead through them what was of course very undesirable. Movable electric heating devices were available too. U 1 didn’t have any wooden wainscoting on the pressure hull and the crew was fully exposed to the condensed water. If you wanted to go to bed, you first had to put the electrical heater in to the bunk to get rid of the moisture in it, and especially in winter to get at least an remote imagination of warmth in it. Than you crawled under the bed cover and spread a big oilcloth over you. When you woke up again, the wrinkles of the oilcloth were full of water and the watch shift always began with a hot cup of coffee. The comfort was very neglected on this type of boats since there were meant to operate only 12 hours on an coastal outpost and then being replaced by another boat, much like the small patrol crafts. But in war they would operate 5 maybe up to 7 days if necessary.

Operational History

U 1 made only few war patrols, in the east sea, without scoring any hits and served most of the time as a training boat. Such legends like Otto Weddingen received their basic training on it.

Design Analysis and Discussion

• Even for a coastal u-boat the tower design don't gave sufficient protection for the crew from the high waves and the corresponding sea spray.
• The lack of e-motors for the planes making it less capable to operate at periscope depth especially in rough seas the operational time at periscope depth would be pretty short.
• Two other disadvantages that made U1 less capable to operate in rough seas at periscope depth were:
  • 1.The only 4 meter long periscope. 4 meters were considered as to short for a save operation at periscope depth in rough seas. After the experience with the first series of kerosene u-boats a length of 6-8 meters were demanded by the u-boat inspection and the crews, for the upcoming designs. However in the case of U 1 and other coastal u-boats it also must be mentioned that in the rather shallow water the waves aren't so high than in the deep Atlantic for example. That compensates the too short periscopes to some extent. But longest possible periscopes are desirable not only because they give to the u-boat better capabilities to operate in rough seas on periscope depth but also because it makes engagements for the u-boat less risky. This becomes obviously when you remember that the optimal attack range for an u-boat was 300m. There is a high risk to approach targets so close, because from this close distance the periscope can be spotted much easier and the biggest danger for an u-boat that attack from such a close distance is to being rammed after its presence and position was detected or coincidentally. This risk grows especially when the u-boat attack a group of ships. And here's where a longest possible periscope might save the u-boat. When the length of the periscope is 6 meters but the draft of the destroyer trying to ram the u-boat is only 4 meters then the u-boat would loose only it's periscope and not the whole boat.
    
  • 2. The flat upper deck that signs the first dozens of u-boats was also disadvantageous for rough seas because when the wave moves upwards it dragged the u-boat towards the surface and increased the risk of broaching the surface. That's why later designs have a more rounded, pipe like hull shape with much smaller flat areas on the deck. And the small size is a general factor that makes it more vulnerable to the drag of vertical wave movements at periscope depth anyway.
• An overall too long diving time of 7-8 minutes(without any preparations), from the order to dive, till it reaches a depth of 9 meters. The ventilation masts that needed to be collapsed before diving and the bridge that needed to be capabilities for dive made it more complicated and longer to prepare the ship for dive. Thus lacking crash dive capabilities. Later all u-boats were upgraded with a WWII like crash dive vent system and then the diving time of U1 when unprepared should become only half as long or even shorter.
• Small safe diving depth of only 30 meters. But in areas for which this boat was made the water isn't deeper anyway. But in a war the boat would be used as demanded so it could always end up in much deeper water.
• Poor armament. Only one torpedo tube and a total of 3 torpedos. No deck gun and not even a machine gun was available.
• No radio equipment. I haven't find any indications that it ever was been upgraded with a radio. Radio equipment was been installed since U 5.
• No UT( underwater telephone ) installation. I also see no evidence that it was equipped with a signal device.
• Fairly slow speed on the surface. The hull wasn't so streamlined like on all later boats. The large length to width ratio further contributes to the resistance.
• Bad efficiency of the adjustable propellers.
• Aft planes aren't in the screw jet.
• The planes could be operated only manually.
• Especially the bow planes are exposed to the rough sea on the surface and could possible be damages from it.
• U 1 was also the only u-boat of the imperial German navy that lacked an air cleaning system. Thus the period of submerged operations is much more limited compared to any later design, which would be not much longer than 10 hours.
• Looks like it lacked a real galley. The galley on the first designs was very provisional and like the radio station grew very slowly from design to design. So in U 1 it was only a corner in the torpedo room.
• The worst live conditions on board.
  • No measures against condensed water. There were no wooden fittings inside the u-boat at all.
  • The officers compartments were not isolated from the crew traffic leading through it.
  • The batteries were installed in the crew compartments
    
    All this made U 1 insufficient for a one week operation. But it also must be said that at the beginning the leadership projected a patrol duration of an u-boat in coastal protection duty not longer then one day. But the necessity of the war quickly demanded much more than that.
• No gyro compass at commission but upgraded later with one.
• Chronometer rendered unreliable by the ship magnetism and electricity.
• Uncertain speed measurement.
• Limited use of the magnetic compass.
• Circumstantial ignition of the kerosene engines(true for all petrol engines ever used on u-boats).
• Operational endurance not more than maybe 5 days.
• All German u-boats in WWI had no echo sounder. Thus making sounding a circumstantial and longer affair.

Although, due to all the mentioned disadvantages, its kerosene motors, that produced a far visible white smoke trail ( at least this problem could be solved by developing a special kerosene type OLEX, which was used only for war patrols because it was more expensive than ordinary kerosene and 3000t of it were stored for war times ). Due to all of its shortcomings it was considered as not suitable for war duty but was nevertheless used when the situation required it.

10,8/8,7 kn