CHRONOLOGY

1925
February	The Reichswehr develops a requirement for a new 3.7cm antitank gun.
1927
June	Heereswaffenamt prioritizes development of a 3.7cm PaK.
1928
January	Rheinmetall completes first 3.7cm PaK L/45 prototype.
1929
May	Rheinmetall begins low-rate production of 3.7cm PaK L/45 antitank gun.
July	Soviet Ministry of Defense authorizes development of heavy tanks.
1930
August 28	Rheinmetall signs secret deal to provide antitank technology to USSR.
December	Soviets begin work on T-30 heavy tank project.
1931
November	OKMO begins building a T-30 prototype.
1932
February	T-30 abandoned; switch to T-35 development.
September	OKMO tests first T-35 heavy tank prototype.
1933
August	Limited production of T-35 begins.
1934
September	Rheinmetall begins conversion of 3.7cm PaK L/45 to upgraded standard.

The first Soviet heavy tank, the multi-turreted T-35, was introduced in 1933. However, the 45-ton T-35 was not a successful design and its thin armor could be penetrated by the German 3.7cm PaK gun at 400m. (Steven Zaloga)

An artillery assembly hall at Rheinmetall-Borsig’s Düsseldorf plant in 1939. Rheinmetall was responsible for designing and manufacturing the bulk of the antitank weapons on the Eastern Front in 1941–43. Like most German industry, Rheinmetall did not gear up for the demands of total war until after the Stalingrad debacle. (Author)

1935
	Rheinmetall begins developing a 5cm PaK.
1937
November	ABTU issues requirement for a new heavy tank resistant to 76mm-gun fire and having a diesel engine.
1938
May	Rheinmetall wins contract to deliver 5cm PaK. OKMO and Kotin teams present SMK and T-100 designs to Defense Council. Stalin approves construction of prototypes.
1939
February	Kotin decides to build single-turret heavy tank (KV).
May	T-100 prototype completed.
August	SMK prototype completed; Stalin approves KV as well. First 5cm PaK 38 prototypes built.
September	KV prototype completed. Trials begin on T-100, SMK and KV-1. Krupp and Rheinmetall begin development of a 75mm PaK gun.
December	SMK, T-100 and KV prototypes see combat in Russo-Finnish War.
December 19	KV-1 approved for production; other two abandoned.
1940
February	Prototypes of KV-2 built.
March	Panzerjäger I with Czech 4.7cm gun on PzKpfw I chassis enters service.
April	KV-1 enters limited production.
May	3.7cm PzGr 40 tungsten-core round enters service.
August	5cm PaK 38 antitank gun enters low-rate production.
1941
May	5cm PzGr 40 round for PaK 38 introduced.
June 27	Special Commission from OKH sent to Heeresgruppe Nord to investigate KV tanks.
November	4.2cm PaK 41 prototype completed.
1942
February	Stielgranate 41 introduced for 3.7cm PaK. 7.5cm PaK 40 antitank gun enters service. 7.5cm PaK 97/38 introduced as stopgap solution.
April	Captured Soviet 76.2mm guns converted into 7.62cm PaK 36(r). First Marder II with 7.62cm PaK 36(r) built.
June	Hitler bans further use of tungsten in antitank ammunition.
August	KV-1S is introduced.
1943
February	Hornisse heavy self-propelled Panzerjäger with 8.8cm gun begins production.
November	8.8cm PaK 43 enters service.