9TP

9TP (code for Polish: dziewięciotonowy polski - "9-tonne Polish") was a Polish light tank of early World War II era. A development of the earlier 7TP tank, it was to replace its predecessor in Polish service in 1940. Due to the outbreak of the war, only a limited number of early prototypes and development versions took part in battles of the Invasion of Poland.

The name of the tank was coined after World War II, technically the modified 7TP tanks were probably to retain the old designation regardless of the modifications. Alternative names include the "7TP wzmocniony", that is a "reinforced 7TP".

In the 1930s the Polish Army and the state-owned Państwowe Zakłady Inżynierii (PZInż) corporation worked on numerous modern medium tank designs that were to replace the 7TP as the main tank in Polish service, such as 10TP and 14TP. While 7TP was relatively modern and much superior to its German equivalents, the German Panzer I and Panzer II, it was based on the ageing Vickers 6-Ton and it was clear that it had limited potential for further improvements. However, as the 10TP and 14TP projects were running behind schedule, in 1938 it was decided to improve on the existing design.

The first modification was a new, more powerful powertrain. The new design could use either the Saurer CT1D diesel engine (license-produced in Poland as PZInż 155) or a modern gasoline engine PZInż 725. Both engines were lighter and smaller than the Saurer VBLDd engine used in 7TP. Because of that the armour could be extended and more space could be redirected to the battle compartment. An additional bonus was the fact that both engines were water-cooled which allowed for the rear grille of 7TP to be replaced with solid armoured plates. Another modification planned for the 9TP was switching from bolted and screwed to welded armoured plates, which further strengthened the hull and allowed to save additional 210 kilograms, enough to further strengthen the armour and widen the tracks from 267 mm to 320 mm.

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