Moonbounce by Accident in 1943

September 27th, 2023

I have been in contact recently with Cindy Stodola Pomerleau, W2AXO, the daughter of Edwin K. Stodola, chief scientist of project Diana, about a text by Dr. Stepp, an engineer of the German Telefunken company, describing reflections from the moon with a radar system in 1943. The text has originally been published in a german nautical journal and been reprinted in CQ DL later. So it is in German only and as I think, it could be of some interest to the moonbounce community, I did a quick translation to English.
Btw.: If interested in Project Diana, the book, written by Cindy, is a must have!

Not much is known about the German technicians picking up reflections from the moon, while testing newly developed radar equipment on the island of Ruegen. Later one of them, Dr. Stepp, published a short report, he wrote:

Back in 1943 Telefunken was to develop a system for detection and measurement of near to ground targets – ships, low-level attack aircrafts and vehicles – with a maximum outreach.

The mission to detect close to ground objects required among high transmission power and receiver sensitivity the use of least possible short waves. As the capabilities of those times allowed, a stationary facility was erected with the following characteristics:

TX pulse power:                  120 kW
Pulse duration:                    1,5 µS
Wavelength:                         53 cm, abt. 564 MHz
RX sensitivity:                      12kTo
Antenna surface:                45 m²
Polarization:                         horizontal
Number of dipoles:            8 per row horizontal
                                          80 per column vertical

The antenna could be turned around the vertical axis. It had a very narrow vertical beam with zeroes in the diagram 1.3° beside the main beam direction.

The system was named Wuerzman. In late 1943 the system was erected in the south of the island of Ruegen on a hill called Bakenberg for field testing.

The results confirmed the reckoned outreach: Ships of mid sizes could be detected up to the horizon at about 50 km, airplanes up to a height of 1000 m and up to a distance of 100 km. Under convenient weather conditions it detected targets in the harbor of Danzig (Gdansk) and the Gulf of Finland.

After the first tests I instructed Willi Thiel, a high-achieving technician, to mind the system by himself and to operate it continuously. A couple of weeks later I returned to the island of Ruegen for tests nearby Goehren. On the last day of my stay, a couple of hours before my journey back to Berlin, I visited the Bakenberg again. The sky was very cloudy and the night extremely dark. On our way to the Bakenberg W. Thiel told me about a strange fault, he mentioned the day before at the same time, but couldn´t find the reason, as after about two hours it gradually declined and at least disappeared.

After starting the operation of the Wuerzmann I made following observation: The fault appeared again, it had a length of several pulses and a bigger pulse amplitude than the strongest close targets. It appeared about two seconds after the start of transmission and disappeared pulsing analogous later after the stop of transmission. All other targets disappeared in the moment of switching off the transmitter. The fault happened only when the antenna beamed east, disappeared at once after larger changes of the bearing and appeared with a two seconds delay when beaming east again. It seemed, we targeted the moon behind the clouds. The degrading disappearance I explained as the slow movement of the reflecting body out of the narrow horizontal pointing beam together with a growing height over the horizon.

Soon after the system went into destinated operation, I never heard of further observations.

German original in: Der Seewart, Band 35, 1974, Heft 2, S. 71
Reprint in CQ DL 1979, Heft 7, S. 328
Translation by Andreas Imse, DJ5AR

A picture of the system can be found here:

Addendum November 6th, 2023

Cindy, W2AXO, did a great job in further investigations and published a very comprehensive history of early moonbounce on her website: