The first U-boats reached US waters on January 13, 1942. By the time they withdrew on February 6, they had sunk 156,939 tonnes of shipping without loss. The first batch of Type IXs was followed by more Type IXs and Type VIIs supported by Type XIV "Milk Cow" tankers which provided refuelling at sea. They sank 397 ships totalling over 2 million tons. (As mentioned previously, not a single troop transport was lost.) In 1943, the United States launched over 11 million tons of merchant shipping; that number declined in the later war years, as priorities moved elsewhere.