Hans Ferdinand Mayer, author of the Olso Report. While British scientist R. V. Jones was able to identify Mayer as the author in 1955, Mayer’s authorship was not revealed to the public until 1989.
Despite its importance to the histography of the Second World War, it is frustratingly difficult to obtain a complete transcript of this document. The original appears to be held at:
Report by Hans Ferdinand Mayer, 5 November 1939, ADM 1/23905, Public Record Office, National Archives (UK).
A full transcript, both in German and English, was ultimately located at V-2Rocket.com. My thanks to their efforts.
The report was submitted anonymously through the British Embassy in (at the time) neutral Norway. The package contained a vacuum tube from a prototype proximity fuse and was signed “a German scientist, who is on your side.”
Pictures shown are purely for educational purposes and no permission has been sought. Blue characters are additions and corrections I have made to the transcript. If any mistakes are found, please let me know by contacting me here.
1. THE JU 88 PROGRAM
Ju 88 is a twin-engine long distance bomber and has the advantage that it can be used as a dive bomber. Several thousand, probably 5,000, are being produced monthly. By April 1940, 25-30,000 of this type are intended to have been produced.
[It is true that bomber production jumped considerably in 1940, however Mayer greatly overestimates his numbers. From 1939 to 1940, production of the Ju-88 jumped from 69 aircraft to 2,208 total (including night fighter and reconnaissance variants).]
2. THE “FRANKEN”
The first German aircraft carrier lies in Kiel harbor. She is to be completed by April 1940 and is named the Franken.
[In reality, Germany had already completed her first carrier, the Graf Zeppelin, which was launched on 8 December 1938. Mayer is actually referencing her sister-ship, the Peter Strasser, then still under construction, and conflated her name with that of the Franken, an oiler also under construction at this time.]
3. REMOTE CONTROLLED GLIDERS
The Kriegsmarine is developing remote controlled gliders, i.e. small aircraft of about three meters wingspan and three meters long, which carry a large explosive charge. They have no engine and are dropped from aircraft from a great height. They contain:
a) An electric altimeter, similar to the radio altimeter [Mayer cites the following article: Lloyd Espenschied and R. C. Newhouse, “A Terrain Clearance Indicator,” Bell System Technical Journal (January 1939): 222-234]. This causes the glider to pull out at about three meters above the water. Then it continues to fly horizontally with rocket propulsion.
b) Remote control by ultra-short waves in the form of telegraphy signals by which the glider can be steered to the right, to the left, or straight ahead, e.g. from a ship or an aircraft. In this manner, the glider is to be aimed at the side of an enemy ship, at which point the explosive charge is to be dropped to explode under water.
The secret number is FZ 21 (Ferngesteuerte Zielflugzeug) [Remote Control Target Aircraft]. The test site is at Peenemünde, at the mouth of the Peene, near Wolgast, in the vicinity of Greifswald.
[It is almost certain that Mayer is referring to the Blohm & Voss BV 143, one of several anti-shipping weapons under development by at this time.]
4. AUTOPILOT
Bearing the secret number FZ 10 an autopilot (remote-controlled aircraft) is being developed in Diepensee near Berlin, which is to be controlled from a manned aircraft to destroy, for instance, barrage balloons.
[It is unclear what program Mayer is referring to here, but an aerial drone program was eventually created in 1941. Called BEETHOVEN, composite aircraft (two aircraft joined together) saw a mothership control and release an attached explosive-filled drone.]
5. REMOTE CONTROLLED PROJECTILES
The Heereswaffenamt (HWA) [Army Ordinance Office] is the development center for the Army. This center is developing projectiles of 80 cm caliber. Rocket propulsion is used; stabilization is by means of built-in gyroscopes. The problem with rocket propulsion is that the projectile does not fly in a straight line but in uncontrollable curves. Therefore it has a radio remote control by which the burn-off of the combustion unit can be steered. This development is only in the initial stages and the 80 cm projectiles are intended to be used later against the Maginot Line.
[Here Mayer fails to mention Germany’s development of liquid-base rocket fuels. This is important as solid-base rockets, then under development in Great Britain, are nowhere near as large as what Mayer describes here – the result being that many in British intelligence question the report’s credibility. While no such rockets are used against the Maginot Line, Mayer’s description resembles that of A-8 rocket.]
6. RECHLIN
This is a small place on the Lake Müritz, north of Berlin. Here are situated the laboratories and development centers of the Luftwaffe, a rewarding target for bombers.
7. METHOD OF ATTACKING FORTIFICATIONS
Experience in the Polish campaign has shown that an ordinary direct attack is useless against fortifications. The Polish fortifications were therefore completely covered with smoke by gas grenades, the smoke being shifted ever deeper into the emplacements. The Polish troops were thus forced to withdraw into the emplacements. Immediately behind the smoke screen, German flamethrowers came forward and took up positions in front of the emplacements. Against these flamethrowers, the emplacements were powerless and the crews either died or surrendered.
8. AIR RAID WARNING EQUIPMENT
At the time of attack by English airmen on Wilhelmshaven in early-September, the English aircraft were already detected when they were still 120 km off the German coast. Along the entire German coast 20 kw short-wave transmitters have been installed, which transmit very short pulses of 10-5 second duration. These pulses are reflected by the aircraft. Close to the transmitter a radio receiver is tuned to the same wavelength. After a certain interval, the pulse reflected by the aircraft arrives at the receiver and is displayed on a cathode-ray tube. From the interval between the transmitted and the reflected pulses, the distance of the aircraft can be calculated. As the transmitted pulse is much stronger than the reflected pulse, the receiver is blocked during transmission. The transmitted pulse is displayed on the cathode-ray tube as a fixed mark.
In connection with the Ju 88 program, such transmitters are to be installed throughout Germany by April 1940.
Countermeasures: With special receivers capable of registering pulses of 10-5 to 10-6 seconds, the wavelength of the pulses transmitted in Germany should be determined and interfering pulses should be transmitted on the same wavelengths. These receivers can be installed on the ground and the same applies to the transmitters, because the method is very sensitive.
While this method is being introduced on a large scale, another method is in the preparatory stage, which uses 50 cm waves…. The transmitter T broadcasts short pulses, which are sharply focused with a concave electric reflector. The receiver R stands immediately next to the transmitter and likewise has a directional antenna. It receives the reflected pulses. T and R are connected by an artificial conductor whose propagation time is continuously variable. This artificial conductor has the following purpose. Normally the receiver is blocked and cannot receive pulses. The radio pulse emitted by T also passes through the artificial conductor and activates the receiver for a very short time. When the propagation time through the artificial conductor equals the time interval before the reflected pulse arrives, the latter can be displayed on the receiver’s cathode-ray tube. With this method, the distance of an aircraft, for example, can be measured very precisely and the method is very insensitive to interference because the receiver is only open for a very short time.
[Mayer’s description of German radar development reveals his background in telecommunications, and while he does not identify its wavelength (1.2 m), the first radar he describes is FREYA. The radar he describes as being under development is WÜRZBURG, which he accurately notes as having a 50 cm wavelength.]
9. AIRCRAFT DISTANCE-MEASURING EQUIPMENT
When airmen carry out an attack on a foreign country, it is important for them to know how far they are from their base. For this purpose, the following invention is being developed at Rechlin:
At the base there is a radio transmitter (6 m band) modulated with an audio frequency “F,” The aircraft, at distance “A,” receives the 6 m wave and demodulation yields the audio frequency “A.” This audio frequency is used to modulate the aircraft’s own transmitter, which is tuned to a slightly different wavelength. This modulated signal emitted by the aircraft is received at the base and demodulated. The resulting audio frequency “F” thus is compared with the local audio frequency. These two differ in the phase angle 4πFA/C, where A = distance of the aircraft; C = speed of light.
By measuring the phase angle, one can therefore determine the distance to the aircraft and can inform the aircraft of its position. For the measurement to be unambiguous, the phase angle must be less than 2tt. One therefore chooses a low frequency, e.g. 150 cps, so that for 1000 kms the phase angle is exactly 2tt. With such a low frequency, no great precision can be attained, however. Therefore a second, higher (e.g. 1500 cps) frequency is transmitted simultaneously and its phase angle is also compared. So 150 cps for coarse, 1500 cps for fine measurement.
By measuring the phase angle, one can therefore determine the distance of the aircraft and can inform the aircraft of its position. For the measurement to be unambiguous, the phase angle must remain below 2π. One therefore chooses a low frequency, e.g. 150 cps so that for 1,000 kms the phase angle is exactly 2π. With such a low frequency, no great precision can be attained, however. Therefore a second, higher (e.g. 1.500 cps) frequency is transmitted simultaneously and its phase angle is also compared. So 150 cps for coarse, 1500 cps fine measurement.
[While Mayer is, in general, describing early German radio direction finding equipment (RDF), the figures he quotes match those of Y-Gerät, a refinement of RDF systems used for blind-bombing.]
10. TORPEDOES
The Kriegsmarine has two new types of torpedo:
a) For instance, it is desired to attack convoys from 10 km distance. Such torpedoes have a radio receiver that can receive three signals. With these signals, the torpedo can be steered to the left, to the right, or straight ahead from the ship that has launched the torpedo or from an aircraft. Long waves are used, which penetrate well under water, order of 3 km. These are modulated by short audio frequency signals which can steer the torpedo. In this manner the torpedo is to be guided to within the vicinity of the convoy. To actually hit a ship, the head of the torpedo contains two acoustic receivers (microphones) which constitute a directional receiver. With this receiver the course of the torpedo is so adjusted that is automatically runs toward the source of the acoustic noise. When the torpedo has been steered by radio to within a few hundred meters of the ship, it automatically runs towards that ship as any vessel will make acoustic noise because of its engines. With acoustic and radio interference, it is relatively easy to protect oneself.
[This is in reference to the G7e (TIV) Falke (Falcon) acoustic torpedo and its replacement, the G7e (TV) Zaunkönig (Wren) – both of which entered service in 1943. The Wren is particularly successful, sinking some 77 vessels before war’s end, though Allied navies quickly respond with noise-maker countermeasures such as FOXER. The US Mk. 24 FIDO, torpedo (deliberately mislabeled as a mine), was based very much on this same concept, and was responsible for sinking a whopping 37 German submarines after its introduction that same year.]
b) The second type of torpedo is probably the one that sank the Royal Oak [Revenge-class battleship sunk on 14 October 1939 by the Type VIIB submarine U-47 off Scapa Flow, Scotland]. These do not hit ship’s hull but explode underneath the ship’s bottom. The detonation is initiated magnetically and is based upon the following principle:
The vertical component of the terrestrial magnetic field is approximately the same everywhere, but it is altered by the ship “S” so that it is weaker at “A” and “C” and stronger at “B.” A torpedo coming from the left first runs in a normal field, then in a weaker one etc.
The head of the torpedo contains a coil rotating about a horizontal axis in the manner of an earth inductor. At the terminals of this coil, a DC voltage is developed, proportional to the vertical component of the terrestrial magnetic field. In series with this voltage, a voltage of equal amplitude but opposite polarity is supplied so that no current can flow while the torpedo runs in the normal terrestrial field. When the torpedo arrives at “A”, however, the magnetic field is smaller and the voltage developed at the rotating coil terminals decreases. The two opposite voltages are no longer equal, current flows and activates a relay, triggering the fuze. A delay has been chosen such that the explosion takes place exactly underneath the ship’s bottom.
Perhaps one can protect oneself against such torpedoes by running a cable along the ship, at about the level of the ship’s bottom and as far away from the hull as possible. When a suitable direct current is passed through this cable, this also creates a magnetic field and the critical point “A” will be shifted to a position far away from the ship. The torpedo will then explode prematurely. Perhaps it is also possible to compensate for the distortion of the magnetic field caused by the great mass of the ship by means of suitably selected compensation coils.
[Magnetic pistol type torpedoes proved notoriously unreliable for all the war’s combatants; even the sinking of the Royal Oak was a something of a fluke, as several of the torpedoes failed to detonate. Magnetic mines were more successful, and Great Britain led in the development of degaussing technology, which ‘wiped’ ships by dragging 2000 amp electrical cables alongside their hulls to reduce their magnetic fields.]
ELECTRIC FUZES FOR BOMBS AND SHELLS
In Germany, mechanical fuzes are being discontinued and the intention is to use electric fuzes instead. All fuzes for bombs are already electrical. Figure 1 shows the principle. When the bomb leaves the aircraft, the condenser “C 1” is charged by a 150 V battery via a sliding contact. This charges the condenser “C 2” via a resistor “R.” “C 2” only becomes charged when the bomb is at a safe distance from the aircraft. When the bomb hits, a mechanical contact “K” closes and the condenser discharges over the ignition coil “Z.” The advantage is that the bomb can never be “live” when it is still attached to the aircraft, which can thus be landed safely with the bombs still on board.
Figure 2 illustrates an electrical time-fuze. This uses the same principle, only instead of the mechanical contact there is a neon lamp “G,” which ignites after a precisely determined interval. This interval can be preset by the values of the condensers and resistances.
The newest development uses neon lamps with grids, Figure 3. When the battery voltage is so chosen that it is just below the ignition voltage and when the grid is insulated, the lamp can be ignited by changes in the partial capacitances “C 12” and “C 23.” Extremely small changes in the partial capacitances are already sufficient. Figure 4 shows the principle of incorporation in a projectile. The head of the projectile “K” is insulated and connected to the grid of the neon lamp. When the projectile passes near an aircraft, for example, the partial capacitances are slightly altered and the neon lamp ignites so that the projectile explodes. Also, the fuze can be so adjusted that all projectiles explode at a precisely determined height above the ground, e.g. at 3 m.
Herewith I enclose such a lamp with grid; there is an improved lamp in which the grid consists of a ring.
The bomb-release fuze bears the number Nr. 25; production is to be increased from 25,000 in October 1939 to 100,000 as from April 1940.
These fuzes are manufactured in Sömmerda, Thüringen, along the railway from Sangerhausen to Erfurt. The firm is called Rheinmetall.
[In fact, several German firms were working toward proximity fuses, with the Rheinmetall Kranich (Crane) acoustic proximity fuse being the most favored design. These were primarily intended for the anti-aircraft role, and had the potential of being used with Germany’s early surface-to-air missile designs. It is fortuitous that German proximity fuze development never progressed past the testing stages. Allied proximity fuzes did enter service, and proved critical in air defense against German V-weapons and Japanese kamikazes.]