Karl Ludwig Föppl (27 February 1887 – 13 May 1976) was a German
mechanical engineer
Mechanical may refer to:
Machine
* Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement
* Mechanical calculator, a device used to perform the basic operations o ...
who succeeded his father,
August Föppl as professor of technical mechanics at the
Technical University of Munich
The Technical University of Munich (TUM or TU Munich; ) is a public research university in Munich, Bavaria, Germany. It specializes in engineering, technology, medicine, and applied and natural sciences.
Established in 1868 by King Ludwig II ...
. During
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
, Föppl worked as a
cryptanalyst
Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic se ...
,
initially in Inspectorate 7/VI, and later in the war within
General der Nachrichtenaufklärung
() was the signals intelligence agency of the German Army (1935-1945), Heer (German Army), before and during World War II. It was the successor to the former cipher bureau known as Inspectorate 7/VI in operation between 1940 and 1942, when it wa ...
.
By 1940, he was a full member of the
Bavarian Academy of Sciences
The Bavarian Academy of Sciences and Humanities () is an independent public institution, located in Munich. It appoints scholars whose research has contributed considerably to the increase of knowledge within their subject. The general goal of th ...
. Föppl was one of the earliest
cryptoanalysts in the
Germany Army, working at this profession during both the first and second world wars, eventually becoming Chief of Sixth Army’s Evaluation Office. His work was kept secret from both his family and his colleagues, even his later university assistant
Friedrich L. Bauer
Friedrich Ludwig "Fritz" Bauer (10 June 1924 – 26 March 2015) was a German pioneer of computer science and professor at the Technical University of Munich.
Life
Bauer earned his Abitur in 1942 and served in the Wehrmacht during World War ...
, who would also become a well known cryptologist in his own right, never knew. In 2005, the work of Hilmar-Detlef Brückner of the Bavarian State Archive () brought this aspect of Föppl's career to prominence. Brückner's work was subsequently fleshed out from information contained in Föppl's unpublished autobiography, still retained by his family, several chapters of which provided details of his work during the two world wars.
Life
Föppl was the son of
August Föppl, a German
structuralist and university lecturer. His brother was
Otto Föppl who was an engineer and Professor of Applied Mechanics at the
Technical University of Braunschweig
TU Braunschweig (, unofficially ''University of Braunschweig – Institute of Technology'') is the oldest ' (comparable to an institute of technology in the American system) in Germany. It was founded in 1745 as Collegium Carolinum and is a membe ...
for 30 years.
His brother-in-law was the
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...
Ludwig Prandtl
Ludwig Prandtl (4 February 1875 – 15 August 1953) was a German Fluid mechanics, fluid dynamicist, physicist and aerospace scientist. He was a pioneer in the development of rigorous systematic mathematical analyses which he used for underlyin ...
. Föppl completed his
Abitur
''Abitur'' (), often shortened colloquially to ''Abi'', is a qualification granted at the end of secondary education in Germany. It is conferred on students who pass their final exams at the end of ISCED 3, usually after twelve or thirteen year ...
in 1906 and studied mechanical engineering for two years at the Polytechnical Institute. He then spent a year at the
University of Göttingen
The University of Göttingen, officially the Georg August University of Göttingen (, commonly referred to as Georgia Augusta), is a Public university, public research university in the city of Göttingen, Lower Saxony, Germany. Founded in 1734 ...
studying the theoretical aspects of engineering. He was promoted in 1912 to
Dr Phil in mathematics, with a thesis titled ''Stable arrangements of electrons in the atom'' ().
He worked as an assistant to
Felix Klein
Felix Christian Klein (; ; 25 April 1849 – 22 June 1925) was a German mathematician and Mathematics education, mathematics educator, known for his work in group theory, complex analysis, non-Euclidean geometry, and the associations betwe ...
, a leading mathematician on
Group theory
In abstract algebra, group theory studies the algebraic structures known as group (mathematics), groups.
The concept of a group is central to abstract algebra: other well-known algebraic structures, such as ring (mathematics), rings, field ( ...
,
complex analysis
Complex analysis, traditionally known as the theory of functions of a complex variable, is the branch of mathematical analysis that investigates functions of complex numbers. It is helpful in many branches of mathematics, including algebraic ...
and
non-Euclidean geometry
In mathematics, non-Euclidean geometry consists of two geometries based on axioms closely related to those that specify Euclidean geometry. As Euclidean geometry lies at the intersection of metric geometry and affine geometry, non-Euclidean ge ...
. In March 1914, Föppl
habilitated
Habilitation is the highest university degree, or the procedure by which it is achieved, in Germany, France, Italy, Poland and some other European and non-English-speaking countries. The candidate fulfills a university's set criteria of excellen ...
in mathematics. He started teaching as a
Privatdozent
''Privatdozent'' (for men) or ''Privatdozentin'' (for women), abbreviated PD, P.D. or Priv.-Doz., is an academic title conferred at some European universities, especially in German-speaking countries, to someone who holds certain formal qualifi ...
at the Physics Institute at the
University of Würzburg
The Julius Maximilian University of Würzburg (also referred to as the University of Würzburg, in German ''Julius-Maximilians-Universität Würzburg'') is a public research university in Würzburg, Germany. Founded in 1402, it is one of the ol ...
, working with
Wilhelm Wien
Wilhelm Carl Werner Otto Fritz Franz Wien (; 13 January 1864 – 30 August 1928) was a German physicist who used theories about heat and electromagnetism to deduce Wien's displacement law, which calculates the emission of a blackbody at any te ...
.
From 1925 to 1955 he was Director of the ''Mechanical-Technical Laboratory'' of the Technical University of Munich.
In July 1918, Föppl became engaged to Friederike Pühn.
Military life
World War I
At the beginning of World War I, Föppl was keen to enlist and experience life at the
front as part of the infantry, but found the process less than straightforward due to the high number of other volunteers enlisting. Peter Vogel, who taught mathematics at the Munich
War Academy (), suggested that Föppl would be more likely to be able to serve if he volunteered to join the wireless telegraphy service, and provided a contact for a colonel in the
Ministry of War. Föppl was successful in enlisting in the Wireless Telegraphy Replacement Company.
After finishing his basic training, Föppl was posted to
Roubaix
Roubaix ( , ; ; ; ) is a city in northern France, located in the Lille metropolitan area on the Belgian border. It is a historically mono-industrial Communes of France, commune in the Nord (French department), Nord Departments of France, depar ...
, arriving on 15 December 1914. The unit's remit was to intercept wireless communications of the
British Expeditionary Force and the ships of the
Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
in the English Channel. However, Föppl ended up working as a kitchen boy, as he was unable to transcribe nonencrypted messages due to his lack of French.
By early 1915, there were thousands of
encrypted
In cryptography, encryption (more specifically, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as plain ...
messages, which were believed by the
German Army
The German Army (, 'army') is the land component of the armed forces of Federal Republic of Germany, Germany. The present-day German Army was founded in 1955 as part of the newly formed West German together with the German Navy, ''Marine'' (G ...
and
German Navy
The German Navy (, ) is part of the unified (Federal Defense), the German Armed Forces. The German Navy was originally known as the ''Bundesmarine'' (Federal Navy) from 1956 to 1995, when ''Deutsche Marine'' (German Navy) became the official ...
to be unusable. Föppl sought permission to attempt to decipher them during his spare time.
Föppl began by determining which messages had been encrypted using the same key; this was accomplished by looking for common sequences of characters. These messages were structured and transmitted in sets of five letters, transcribed on square paper, and each message was represented as a series of columns of letters. As an emergent property of this transcribing method, standard sequences of characters stood out readily.
Foppl focused on groups of four or more characters. When a sequence appeared more than once in a message, or in several messages, he indicated that it was enciphered with the same key. Having sorted all the messages into groups, he focused on the group which seemed easiest to
analyse as it contained the largest number of messages and the most repetitions of common sequences. He used
frequency analysis
In cryptanalysis, frequency analysis (also known as counting letters) is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.
Frequency analysis is based on th ...
against the message, then compared it against the equivalent statistics for a
plaintext
In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted.
Overview
With the advent of comp ...
English document. He was able to instantly determine the key. Since this key was still in use, the Roubaix station was able to start reading incoming messages that were encrypted with that key.
The news of the deciphering spread rapidly through the German Navy. The majority of the decrypts were related to British
minesweeping operations in the
English Channel
The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...
.
The key that Föppl discovered was termed a ''Caesar'' and the cipher was a variant of the
Gronsfeld cipher. Föppl suggested it was used as it enabled the cipher clerk to encrypt messages very quickly and could be easily enciphered by ordinary sailors, with a key that was changed every few weeks, that could be broken within a single day.
During this period Föppl read the lengthy daily telegrams sent by
Second Sea Lord
The Second Sea Lord and Deputy Chief of the Naval Staff (formerly Second Sea Lord) is deputy to the First Sea Lord and the second highest-ranking officer currently to serve in the Royal Navy and is responsible for personnel and naval shore estab ...
George Egerton and managed to break the cipher, known as the
Allied Fleet Code that was long considered unbreakable by the German Navy, and was considered thus to be a new source of intelligence which was of the greatest importance. From July 1915, daily reports compiled by Foppl and Lieutenant Martin Braune, the director of marine intelligence (
German Naval Intelligence Service), were now sent to senior staff.
Vizeadmiral Hugo von Pohl stated:
:''They have proved to be a great help for our submarine and Zeppelin missions.''
Föppl was promoted to sergeant () on 9 January 1916 and subsequently promoted to
Lieutenant
A lieutenant ( , ; abbreviated Lt., Lt, LT, Lieut and similar) is a Junior officer, junior commissioned officer rank in the armed forces of many nations, as well as fire services, emergency medical services, Security agency, security services ...
on 14 July 1916, which was subsequently converted into a full
commissioned officer post in the regular army on the August 1918. His promotion enabled him to build a small team which included physicists
Wilhelm Lenz and . Föppl found that due to his work, he was able to rescue academically gifted individuals from the front line, for use as cryptanalysts and evaluators, an idealised sentiment which was not always successfully achieved. The mathematician
Richard Courant
Richard Courant (January 8, 1888 – January 27, 1972) was a German-American mathematician. He is best known by the general public for the book '' What is Mathematics?'', co-written with Herbert Robbins. His research focused on the areas of real ...
offered several suggestions to Föppl, including one individual whom he arranged to be transferred to the unit but he was killed in action before the transfer could be completed. By the end of World War I, Föppl was head of
Sixth Army’s Evaluation Office, located in
Lille
Lille (, ; ; ; ; ) is a city in the northern part of France, within French Flanders. Positioned along the Deûle river, near France's border with Belgium, it is the capital of the Hauts-de-France Regions of France, region, the Prefectures in F ...
and then
Tournai
Tournai ( , ; ; ; , sometimes Anglicisation (linguistics), anglicised in older sources as "Tournay") is a city and Municipalities in Belgium, municipality of Wallonia located in the Hainaut Province, Province of Hainaut, Belgium. It lies by ...
.
Föppl was demobilized at the end of hostilities.
World War II
In March 1938, Föppl was reactivated and told to report to Army HQ after the
Anschluss
The (, or , ), also known as the (, ), was the annexation of the Federal State of Austria into Nazi Germany on 12 March 1938.
The idea of an (a united Austria and Germany that would form a "German Question, Greater Germany") arose after t ...
, where he was sent to Vienna to work at a German wireless company. Upon arrival, there was some confusion as to his purpose, since he was then in his mid 50s, with no modern uniform, and had spent the interwar period employed as an academic. He was ordered to visit the
TU Wien, where he meet the Rector of the Institute and attended a meeting of the Senate to answer extensive questions from staff and academics about the Anschluss. After a week, he was demobilized and sent back to Munich.
On 25 August 1939, Föppl was again reactivated and requested (ordered) to Army HQ in Berlin for assignment, which put his whole family into a deep depression. Föppl was assigned an Evaluation Office working on the
Invasion of Poland
The invasion of Poland, also known as the September Campaign, Polish Campaign, and Polish Defensive War of 1939 (1 September – 6 October 1939), was a joint attack on the Second Polish Republic, Republic of Poland by Nazi Germany, the Slovak R ...
. He asked to be posted closer to his family and was eventually posted to western Army HQ in
Frankfurt
Frankfurt am Main () is the most populous city in the States of Germany, German state of Hesse. Its 773,068 inhabitants as of 2022 make it the List of cities in Germany by population, fifth-most populous city in Germany. Located in the forela ...
, working in a cryptanalysis role. He subsequently made a request to move back to work at the
Technical University of Munich
The Technical University of Munich (TUM or TU Munich; ) is a public research university in Munich, Bavaria, Germany. It specializes in engineering, technology, medicine, and applied and natural sciences.
Established in 1868 by King Ludwig II ...
and was discharged on 20 January 1940, with his military career at an end. He spent the rest of the war continuing his research at the university, deliberately keeping a low profile.
Academia
After the military service in World War I, Ludwig Föppl became professor of mechanics at the Technische Hochschule Dresden in 1920 and professor of mechanics at the Technische Hochschule Munich in 1922. The focus of his works was on theoretical continuum mechanics. Apart from this, Föppl has significantly developed the industrial measuring technique of
photoelasticity
In materials science, photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a ...
in Germany. During the Second World War, he relocated his residence and photoelasticity laboratory to Ammerland, which may have saved his life, because his house in Munich was hit by an American bomb in an attack on July 12, 1944, and was completely destroyed.
It was his photoelasticity laboratory, which gave him the possibility to continue working in the first years of the Second World War.
Föppl made an essential contribution to
contact mechanics
Contact mechanics is the study of the Deformation (mechanics), deformation of solids that touch each other at one or more points. A central distinction in contact mechanics is between Stress (mechanics), stresses acting perpendicular to the cont ...
, even when this part of his work became acknowledged only in the last years. The key contribution is contained in his 8-page paper "Elastic stress in the ground under foundations" of 1941. In this paper, Föppl determined the deformation of the surface of an elastic half-space under the action of arbitrary plane as well as arbitrary axis-symmetric pressure distribution, in a form that allowed a simple inversion and thus solution of an arbitrary contact problem. This inversion was made in the dissertation of his doctoral student Gerhard Schubert, published in a shortened form in 1942.
Bibliography
He was editor of the later editions of ''Vorlesungen über Technische Mechanik''
of his father August Föppl (with Otto Föppl) and co-author of ''Drang und Zwang''.
*
*
*
*
*
*
Awards and honours
*
Iron Cross
The Iron Cross (, , abbreviated EK) was a military decoration in the Kingdom of Prussia, the German Empire (1871–1918), and Nazi Germany (1933–1945). The design, a black cross pattée with a white or silver outline, was derived from the in ...
, Second Class - 4 July 1915
*
Iron Cross
The Iron Cross (, , abbreviated EK) was a military decoration in the Kingdom of Prussia, the German Empire (1871–1918), and Nazi Germany (1933–1945). The design, a black cross pattée with a white or silver outline, was derived from the in ...
, First Class - 16 April 1916
*
Military Merit Order, Fourth Class With Swords - 16 April 1916
*
Military Merit Order, Third Class With Swords - 12 September 1916
See also
*
Bearing capacity
*
Method of Dimensionality Reduction
*
Triakis truncated tetrahedron
References
Further reading
* Hilmar-Detlef Brückner: Germany's First Cryptanalysis on the Western Front – Decrypting British and French Naval Ciphers in World War I.
Cryptologia
''Cryptologia'' is a journal in cryptography published six times per year since January 1977. Its remit is all aspects of cryptography, with a special emphasis on historical aspects of the subject. The founding editors were Brian J. Winkel, Davi ...
.
Rose-Hulman Institute of Technology.
Taylor & Francis
Taylor & Francis Group is an international company originating in the United Kingdom that publishes books and academic journals. Its parts include Taylor & Francis, CRC Press, Routledge, F1000 (publisher), F1000 Research and Dovepress. It i ...
,
Philadelphia
Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...
PA 29.2005,1 (January), S. 1–22. ISSN 0161-1194.
* Martin Samuels: Ludwig Föppl – A Bavarian cryptanalyst on the Western front. Cryptologia, 2016. doi:10.1080/01611194.2015.1084960
* Elena Popova, Valentin L. Popov: Ludwig Föppl and Gerhard Schubert: Unknown classics of contact mechanics, Z Angew Math Mech.2020; 100: e202000203. https://doi.org/10.1002/zamm.202000203
External links
*
{{DEFAULTSORT:Foppl, Ludwig
1887 births
1976 deaths
German cryptographers
German mechanical engineers
Engineers from Berlin
Presidents of the Technical University of Munich