From the 14 May, both sides started a mine war, while above ground the attackers were exposed more and more to the fire of the defenders. The latter dug tunnels to undermine the offensive positions and allowed these to collapse. The besiegers especially came under fire from the redoubts, which therefore became the main target of the guns. On 18 May the French gained entry to one of the partly underground passages of Redoubt Mary, and embittered close combat ensued. The next day, the French expelled the defenders from the redoubt. The Spanish had prepared to blow up the position before leaving, but this failed.