In 1933 , when Hitler came to power, Waffenamt ordered the production of 4-7ton Kleintraktor Landwirtschaftlicher Schleppen/ Las agricultural Tractor. All German tank projects were named Agricultural Traktors because of the Versailles treaty which banned Germany from further developments of heavy weaponary. Rheinmetall Borsig, Henschell , MAN , Krupp and Daimler Benz brovided designs and protypes of the Vehicle.All the designs were similar to each other but finally Krupp's design was accepted. After several modifications it was decided to use daimler Benz's turret on Krupp's Chassis. in Febraury 1934 the Las was renamed to Panzer I and entered production in April. First a series of 15 units were produced and were shown to Adolf Hitler by Guderian and after that entered mass production.
The first series was called Ausf A and was produced from July 1934 until June 1936. Ausf B entered production in August 1935 until June 1937. Ausf had an under power engine. it was very noisy and was produced by Krupp. The engine was replaced in Ausf B with 100hp Maybach engine.. Except for the engine Ausf A and Ausf B were almost Identical. Ausf B was just alittle longer than Ausf A because of additional road wheel and the new engine. Both versions were armed with 2 MG34 7.92mm able to fire 650 rounds per minute. Also some of the units were produced without turrets and were used as trainig tanks .
Panzer I first saw combat during the Spanish Civil war (1936-1938). 106 German tanks saw service during this war in Legion Condor helping Franco's nationalist army. The german tanks were completely outclassed by their soviet counterpart ( T26 & BT5) who were serving in the Republican Army. although the spanish civil war showed that the German tanks are no match for any thing more than small fire arms , the highcommand used it as a testing ground for newly developed tactics of the blitzkrieg.
The Panzer I was outclassed by the beginning of the WW2 but it was widely used during the Polish and French Campaigns and even earlt stages of operation Barbarossa . after invading the soviet union they were withdrwn from the front lines and were used against Partisans and also used by the German police in occupied territories. From 1942 until 1943 All PanzerI were converted to ammunition carriers. Some of Ausf Bs were converted as Command Vehicles in Panzerjager Battalions by installing additional radio equippment.
( Heavy armored infantry support tank)