The Armed Forces of Ukraine use an M-240 mortar of 240 mm caliber to fire at the russian invasion forces, as we can see from the photo found on the web.
This mortar system can rightly be called a "museum" weapon, because in Ukraine, it can only be found in a museum or also at a military training base. There is no data whether any of those were kept at the reserve stocks of the AFU. Mass production of this mortar continued through years 1951–1958; over that period, a total of 329 units were manufactured.
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As soon as more advanced and modern "Tyulpan" self-propelled started were introduced, the Soviet army gradually abandoned the M-240. Consequently, these mortar systems were officially withdrawn from service by the russian army as well. The M-240 remains in service only with the armies of Iraq and the regime of Bashar al-Assad in Syria.
Twitter community Ukraine Weapons Tracker suggests that in the warstocks of the Ukrainian Armed Forces there could be a sufficiently large number of 240-mm mortar rounds, apparently even some 3F2 active-reactive shells and 3F5 guided shells of the Soviet "Smelchak" system. Although there are no "Tyulpan" self-propelled mortars in service with the Armed Forces of Ukraine.
But there's a catch: the M-240 has a declared firing range of 10km, with a rate of fire one round per minute, and the round can be inserted only from the muzzle.
Thus the M-240 can only fire under the condition that the enemy cannot engage in a counter-battery combat. And it must be in the very "friendly" conditions somewhere on the southern frontline, where Ukrainian troops can "without haste" one shell after another, since it is one of the most stable areas of the front with Ukrainian forces steadily grinding russian occupiers on the right bank of the Dnipro river, isolated from their supplies.
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