The German U-boat force was primarily based at Ostend, Belgium so that German submarines had better access to the sea lanes around England. The Germans made use of the advantage and sent out about 20 U-boats to begin the naval blockade. In January, before the declaration of "unrestricted submarine warfare", as the submarine blockade was called, 43,550 tonnes of shipping had been sunk by U-boats. The number of sinkings then steadily increased, with 168,200 tonnes going down in August.