As they wait for frozen ground to open a new round of mechanized offensives, Ukrainian and Russian forces have returned to grueling artillery exchanges across the front line, Newsweek reports.

While both sides are facing extreme ammunition pressures, Ukraine is in the unique position of trying to refill its stocks of Soviet-made 152 mm caliber shells, while also working to integrate a variety of NATO-provided artillery systems that mostly fire 155 mm ammunition.

One Ukrainian commander stationed along the southern front told Newsweek that Western shells and artillery systems have been essential in helping the Ukrainians inflict severe casualties on invading Russians.

"The HIMARS [High Mobility Artillery Rocket System] have been a game changer over the summer period," Roman Kostenko said. Kostenko is a veteran of the yearslong fight against Russian-directed forces in the Donbas and is now a member of the Ukraine Parliament.

"Lately, the high-caliber stuff has been hugely helpful: the Excalibur [GPS-guided, U.S.-made shell], in particular, the 155 mm, has shown itself to be very effective, destroying vehicles from a distance and dealing heavy losses to the enemy," he added.

Kostenko noted that his section of the southern front around Kherson is under constant Russian artillery fire and airstrikes and said that Ukraine is always in need of new arms.

"The main issue for us is securing the necessary resources, including weapons and ammo, because the fact is the Russians still have a huge advantage in terms of vehicles, missiles, and ammo, even as our Western allies continue to provide support," he said.

Artillery, in particular, is urgently needed. While requesting more 152 mm shells from allied nations, Ukraine has also been opening new internal supply lines, according to Newsweek. Production limitations will take time to remove, however.

Gustav Gressel, a senior policy fellow at the European Council on Foreign Relations, told Newsweek that "there are certain existing production lines" in countries like Poland, Bulgaria, Romania and the Czech Republic "that have certain capacities, even if you let people work on the weekends and pay them through."

"The defense industries in these countries were basically producing shells for domestic consumption and a bit for exports," Gressel said. "But not to sustain an army as large as the Ukrainian one in a full-scale war against a mobilized Russian army."

The NATO shell supply line is flowing now, Gressel said, but the assorted systems the Ukrainians are working with complicate matters, as not all 155 mm systems can fire the same ammunition at the same rate. The German PzH 2000, for instance, is known to be sensitive to heavy use.

Gressel also said there are fewer 155 mm shells available than 152 mm, but the precision of the Western munitions compensates somewhat for the shortage.

"They are actually quite happy with what they got from NATO," he said.

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