Since May 1861 when England recognized the belligerent rights of the Confederacy, many a foreign ship had run the Union blockade of the Southern coastline which stretched from the Chesapeake Bay to the mouth of the Rio Grande River.
Just across the Rio Grande and outside the jurisdiction of the Union blockade, Matamoras, Mexico maintained a lively trade between the Confederacy and many European nations.
By March 1863, 92 vessels were reported lying off the Rio Grande, and in April Commodore Henry Morris, senior naval officer in New Orleans, ordered a Union warship to Matamoras to drive off those ships, particularly those “which carry English colors, but are not entitled to wear any, and have no legitimate papers, their cargoes being intended to be run over the boundary line into Texas."