This is the Trumpeter 02317 kit in 1/35 scale, of the ‘German 128mm PaK 44’.
The 12.8 cm Pak 44, (Panzerabwehrkanone) was a German anti-tank gun used during World War II.
It was designed as a result of experiences on the Eastern front in 1943. The German army had encountered the Russian 122 mm guns and had issued a requirement for a similar weapon.
Development initially concentrated on a field gun known as the Kanone K 44. However once heavier Russian armour such as the IS-2 started to appear the design requirements were altered to include an anti-armour role.
Source: Trumpeter website