They first appeared as a cloud of dust on the horizon. A few seconds later, the motorcycles carrying Russian soldiers sped into view, zigzagging across a field, kicking up dust, attempting a noisy, dangerous run at a Ukrainian trench.

“They moved fast, they spread out and they swerved,” said Lt. Mykhailo Hubitsky, describing the Russian motorcycle assault he witnessed. It’s a type of attack that has been proliferating along the frontline this spring, adding a wild new element to the already violent, chaotic fighting.

Russian soldiers riding motorcycles, dirt bikes, quadricycles and dune buggies now account for about half of all attacks in some areas of the front, soldiers and commanders say, as Moscow’s forces attempt to use speed to cross exposed open spaces where its lumbering armored vehicles are easy targets.

These nonconventional vehicles have been turning up with such frequency that some Ukrainian trenches now overlook junk yards of abandoned, blown up off-road vehicles, videos from reconnaissance drones show.

The new tactic is the latest Russian adaptation for a heavily mined, continually surveilled battlefield, as Moscow’s forces work to achieve small tactical gains, often of just a few hundred yards.