The strong defences built during the First World War had fallen into disrepair. Defence against air attack was inadequate and blockships sunk to stop U-boats from penetrating had largely collapsed. While there were anti-submarine nets in place over the three main entrances, they were made only of single-stranded looped wire; there was also a severe lack of the patrolling destroyers and other anti-submarine craft that had previously been available. Efforts began belatedly to repair peacetime neglect, but were not completed in time to prevent a successful penetration by enemy forces.