As the war progressed and more Union warships became available for the blockade and the number of available ports became fewer and fewer. But blockade running became more specialized. In 1863, 199 blockade runners arrived in Confederate ports. In 1864 the number grew to 244. In 1865, by the end of the war another 30 had successfully carried their cargoes to Southern ports. More and more this depended on a very special type of ship. They were steamers, built for speed, they had large cargo capacities and had a very low silhouette making them harder to see at a distance. The work was dangerous but a successful trip could gain enormous profits for the crews. They became the South's main outlet for trade with Europe. Without them the Confederacy could not have lasted as long as they did. Risking war with the United States, England secretly built several blockade runners for the South.