As the UK and other European nations prepare to send tanks to Ukraine to help it liberate more territory from Russia, our correspondent Andrew Harding has been to visit members of a front-line Ukrainian tank unit already engaging Russian forces near the fiercely contested towns of Bakhmut and Soledar.
The explosions come every few seconds, sometimes in rapid clusters of six or more short blasts, sometimes deep and long and rib-cage-rattling, thundering across the snow-speckled hills that stretch along the front lines close to Bakhmut and Soledar.
Then come the distant booms, the shorter punch of a mortar round blasting off on the roadside, and, occasionally, the bone-chilling, fizzing whoosh of an incoming artillery shell that sends us diving for cover on the frozen fields.
This is the daily, constant, percussive chorus of war in the Donbas, where Ukrainian and Russian artillery, rocket and tank crews are slugging it out, trading blows in a fierce, but largely inconclusive struggle to break a months-long deadlock.