American merchant shipping had been protected by the British Navy, and as a consequence of the Treaty of Paris and the disarmament of the Continental Navy, the United States no longer had any protection for its ships from pirates. The fledgling nation did not have the funds to pay annual tribute to the Barbary states , so their ships were vulnerable for capture after 1785. By 1789, the new Constitution of the United States authorized Congress to create a navy, but during George Washington's first term (1787–1793) little was done to rearm the navy.  In 1793, the French Revolutionary Wars between Great Britain and France began, and a truce negotiated between Portugal and Algiers ended Portugal's blockade of the Strait of Gibraltar which had kept the Barbary pirates in the Mediterranean. Soon after, the pirates sailed into the Atlantic, and captured 11 American merchant ships and more than a hundred seamen. 
Today ships are significantly faster than in former times, thanks to much improved propulsion systems. Also, the efficiency of the engines has improved, in terms of fuel, and of how many sailors it takes to operate them. In World War II, ships needed to refuel very often. However, today ships can go on very long journeys without refueling. Also, in World War II, the engine room needed about a dozen sailors to work the many engines, however, today, only about 4–5 are needed (depending on the class of the ship). Today, naval strike groups on longer missions are always followed by a range of support and replenishment ships supplying them with anything from fuel and munitions, to medical treatment and postal services. This allows strike groups and combat ships to remain at sea for several months at a time.