In World War 2 why did Germans bomb ports?

1. To disrupt the import of supplies (food, medicines, vital goods, raw materials and so on). If ships bringing supplies to us were unable to dock then rationing of food and other supplies would be even worse than it was - eventually the nation would starve. 2. To disrupt the export of materials and other things. Weapons and ammunitiom left the country to supply the troops abroad. If supplies were cut off then the troops would be defenceless.