From The Civil War at Sea, by Craig L. Symonds (Praeger, 2009), Kindle Locs. 1238-1257:
Altogether during the war, eight Confederate commerce raiders captured and destroyed some 284 Union merchant ships valued at more than $25 million. Most of them were sailing ships, and a third of them (97) were taken by either the Alabama or the Florida.
In assessing the impact of these rebel raiders, as in assessing the impact of the blockade, numbers alone cannot tell the full story. William Dalzell, whose 1940 history The Flight from the Flag remains a classic, argued that the ripple effect of those 284 lost ships went well beyond the immediate impact of sunken ships and lost cargoes. The success of the Florida and the Alabama in particular led to a significant jump in maritime insurance rates, which reduced the profit margin even for ships that never encountered a rebel raider. Moreover, the rebel raiders engendered such fear within the American maritime community that many merchants abandoned American-flag ships altogether and shipped their goods in foreign bottoms. Facing a dearth of customers, American shippers either sold out or reregistered their ships in foreign countries. Whereas in 1858 only 33 American-built vessels registered as British ships, a total of 348 did so in 1863. Thus while the raiders sank or burned some 150,000 tons of Union shipping, they were also instrumental in provoking the transfer of another 800,000 tons to foreign registry. In all, nearly a million tons of merchant ships-half of the U.S. merchant marine-ceased to fly the American flag. In the fall of 1863, a reporter for the New York Herald noted that of the 176 ships then in New York Harbor, only 19 of them flew the American flag. The others flew the flags of England (93), Bremen (20), France (10), Denmark (6), Hanover (6), Hamburg (6), Prussia (4), Belgium (3), Norway (3), Austria (3), Holland (2), and Sweden (1). Indeed, American-flag shipping dropped nearly as spectacularly during the war as southern cotton exports. While the blockade reduced southern cotton exports from 2.8 million bales in 1860 to 55,000 in 1862, rebel commerce raiders effectively reduced Union shipping from 2.2 million tons in 1860 to fewer than 500,000 by 1865. Considering that the South invested considerably less in building and equipping its handful of raiders than the North did in establishing and maintaining the blockade, the southern decision to adopt a strategy of guerre de course [war on commerce] seems more than validated.
On the other hand, the raiders’ impact on the economy of the North was not nearly as devastating as the impact of the blockade was to the economy of the South. The hundreds of American-owned ships that adopted foreign registry to avoid being targeted by the rebel raiders were not lost, merely reflagged. During Britain’s wars with France earlier in the 19th century, much of its trade shifted to American-flag vessels to prevent their capture by French privateers. American commerce in this period had thrived as a result, but so, too, had the British economy. Now the situation was reversed, and during the Civil War much of America’s trade shifted to British-flag vessels. In both cases, the home economy continued to prosper. An editorial in the New York Sun in March of 1865, only weeks before Appomattox, noted “There never was a time in the history of New York when business prosperity was more general, when the demand for goods was greater, and payments more prompt, than within the last two or three years.