Over the weekend, the U.S. government released imagery it cited as evidence that Russia had conducted cross-border shelling into Ukraine. The pictures are grainy but a closer look indicates that the shelling, if carried out by the Russians, could mark a significant escalation in their involvement in the region, as the images depict a concentrated and well-executed attack.

(Courtesy U.S. intelligence community.)

The above images show what appear to be a strike on a bivouacked Ukrainian mechanized unit, with random tire marks (above left) leading into the field, suggesting that units had been holding in position temporarily.

The craters from the artillery appear to be more dispersed to the south, with a tighter concentration to the north, indicating that the fire was “walked” toward its target. This method of targeting is consistent with the orientation of the Russian self-propelled artillery units (above right), as their gun-target-lines are oriented north, the same direction of the shell craters.

When artillery is “walked on” target, the rounds usually fall short until a forward observer near the target adjusts the coordinates for the gun line through a series of corrections. Once the fire is accurate enough, the forward observer would then have the artillery “fire for effect,” hitting the target with a concentrated barrage. These images are consistent with this method, however it is unclear if whoever was firing the artillery had a forward observer on the ground radioing back to the artillery unit or, potentially, an aircraft watching the fall of the rounds.

While the images are of low resolution, the six artillery pieces appear to be a variant of the 2s19 Msta-S, a 152mm self-propelled artillery piece that has been in use by the Russian military since the late 1980s. The 2s19 is easily identifiable by its large turret mounted to the rear of the driver’s compartment. It is loaded manually, with one round for every round fired, although newer variants have an auto-loading feature than can allow the system to fire between six and eight rounds per minute, according to London-based defense consultancy IHS Janes.

Depending on the type of shell loaded, the 2s19 can hit targets up to nearly 25 miles away.