I do not know this maybe the best tank.... first mobile artillery piece Assault artillery...
en.wikipedia.org
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The Sturmgeschütz III (StuG III) assault gun was Germany's most-produced fully tracked armoured fighting vehicle during World War II, and second-most produced German armored combat vehicle of any type after the Sd.Kfz. 251 half-track. It was built on the chassis of the proven Panzer III tank, replacing the turret with an armored, fixed superstructure mounting a more powerful gun. Initially intended as a mobile assault gun for direct-fire support for infantry, the StuG III was continually modified, and much like the later Jagdpanzer, was employed as a tank destroyer.
The Sturmgeschütz originated from German experiences in World War I, when it was discovered that, during the offensives on the Western Front, the infantry lacked the means to effectively engage fortifications. The artillery of the time was heavy and not mobile enough to keep up with the advancing infantry to destroy bunkers, pillboxes, and other minor fortifications with direct fire. Although the problem was well known in the German army, it was General Erich von Manstein who is considered the father of the Sturmartillerie (assault artillery). The initial proposal was from von Manstein and submitted to General Ludwig Beck in 1935, suggesting that Sturmartillerie units should be used in a direct-fire support role for infantry divisions. On 15 June 1936, Daimler-Benz AG received an order to develop an armoured infantry support vehicle capable of mounting a 7.5 cm (2.95 in) calibre artillery piece. The gun mount's fixed, fully integrated casemate superstructure was to allow a limited traverse of a minimum of 25° and provide overhead protection for the crew.[4] The height of the vehicle was not to exceed that of the average soldier.
Snip...
The Sturmgeschütz III-series of vehicles proved very successful and served on all fronts, from Russia to North Africa and Western Europe to Italy, as assault guns and tank destroyers. Because of their low silhouette, StuG IIIs were easy to camouflage and be hidden and were difficult targets to destroy. As of 10 April 1945, there were 1,053 StuG IIIs and 277 StuH 42s in German service.
The StuG assault guns were cost-effective compared to the heavier German tanks such as the Tiger I and the Panther, although as anti-tank guns they were best used defensively as the lack of a traversable turret and its generally-thin armour was a severe disadvantage in the attack role. As the situation for the German military deteriorated further later in the war, more StuGs were built than tanks, particularly due to its ease of production.
In 1943 and 1944, the Finnish Army received 59 StuG III Ausf. Gs from Germany and used them against the Soviet Union. Thirty of the vehicles were received in 1943 and a further twenty-nine obtained in 1944. The first batch from 1943 destroyed at least eighty-seven enemy tanks for a loss of only eight StuGs (some of which were destroyed by their crews to prevent enemy capture).
[7] The later batch from 1944 saw no real action. After the war, the StuGs were the main combat vehicles of the Finnish Army up until the early 1960s when they were phased out. These StuGs gained the nickname "Sturmi" in the Finnish military, which can be found in some plastic scale-model kits.