the German conquest of Western Europe, the air and submarine offensive against British sea communications became much more dangerous than the German offensive during the First World War. Liverpool and its port became an important destination for convoys heading through the Western Approaches from North America, bringing supplies and materials. The considerable rail network distributed to the rest of the country. Air attacks sank of shipping, with another damaged. Minister of Home Security Herbert Morrison was also worried morale was breaking, noting the defeatism expressed by civilians. Other sources point out that half of the 144 berths in the port were rendered unusable and cargo unloading capability was reduced by 75 percent. Roads and railways were blocked and ships could not leave harbour. On 8 May 1941, 57 ships were destroyed, sunk or damaged, amounting to . Around 66,000 houses were destroyed and 77,000 people made homeless ("bombed out"), with 1,900 people killed and 1,450 seriously hurt on one night. Operations against London up until May 1941 could also have a severe impact on morale. The populace of the port of Hull became "trekkers", people who made a mass exodus from cities before, during and after attacks. The Luftwaffe attacks failed to knock out railways or port facilities for long, even in the Port of London, a target of many attacks. The Port of London, in particular, was an important target, bringing in one-third of overseas trade. On 13 March, the upper Clyde port of Clydebank near Glasgow was bombed (Clydebank Blitz). All but seven of its 12,000 houses were damaged. Many more ports were attacked. Plymouth was attacked five times before the end of the month while Belfast, Hull, and Cardiff were hit. Cardiff was bombed on three nights; Portsmouth centre was devastated by five raids. The rate of civilian housing loss was averaging 40,000 people per week dehoused in September 1940. In March 1941, two raids on Plymouth and London dehoused 148,000 people. Still, while heavily damaged, British ports continued to support war industry and supplies from North America continued to pass through them while the Royal Navy continued to operate in Plymouth, Southampton, and Portsmouth. Plymouth in particular, because of its vulnerable position on the south coast and close proximity to German air bases, was subjected to the heaviest attacks. On 10/11 March, 240 bombers dropped 193 tons () of high explosives and 46,000 incendiaries. Many houses