In March, a massive artillery bombardment by the Viet Minh ensued. The strategic positioning of their artillery made it nearly impervious to French counter-battery fire. Tenacious fighting on the ground ensued, reminiscent of the trench warfare of World War I. At times, the French repulsed Viet Minh assaults on their positions while supplies and reinforcements were delivered by air. As key positions were overrun, the perimeter contracted, and the air resupply on which the French had placed their hopes became impossible. As the Viet Minh anti-aircraft fire took its toll, fewer and fewer of those supplies reached the French. The garrison was overrun in May after a two-month siege, and most of the French forces surrendered. A few of them escaped to Laos. The French government in Paris then resigned, and the new Prime Minister, the left-of-centre Pierre Mendès France, supported French withdrawal from Indochina.