Here is the Secretary of the Navy's General Instructions to the blockading squadrons in regards to the "right of search" and I believe the first time the U.S. authorized seizures under the "continuous voyage" doctrine:
General instructions from the Secretary of the Navy to Flag-officers commanding blockading squadrons, regarding the right of search.
NAVY DEPARTMENT, August 18, 1862.
SIR: Some recent occurrences in the capture of vessels and matters pertaining to the blockade render it necessary that there should be a recapitulation of the instructions heretofore from time to time given, and also of the restrictions and precautions to be preserved by our squadrons and cruisers.
It is essential in the remarkable contest now waging that we should exercise great forbearance with great firmness and manifest to the world that it is the intention of our Government, while asserting and maintaining our own rights, to respect and scrupulously regard the rights of others. It is in this view that the following instructions are explicitly given:
First. That you will exercise constant vigilance to prevent supplies of arms, munitions, and contraband of war from being conveyed to the insurgents, but that under no circumstances will you seize any vessel within the waters of a friendly nation.
Secondly. That, while diligently exercising the rights of visitation on all suspected vessels, you are in no case authorized to chase and fire at a foreign vessel without showing your colors and giving her the customary preliminary notice of a desire to speak and visit her.
Thirdly. That, when that visit is made, the vessel is not then to be seized without a search carefully made so far as to render it reasonable to believe that she is engaged in carrying contraband of war for or to the insurgents and to their ports directly, or indirectly by transshipment, or otherwise violating the blockade, and that if, after visitation and search, it shall appear to your satisfaction that she is in good faith and without contraband, actually bound and passing from one friendly, or so-called neutral, port to another, and not bound or proceeding to or from a port in the possession of the insurgents, then she can not be lawfully seized.
Fourthly. That, to avoid difiiculty and error in relation to papers which strictly belong to the captured vessel, and mails that are carried, or parcels under official seals, you will, in the words of the law, preserve all the papers and writings found on board and transmit the whole of the originals unmutilated to the judge of the district to which such prize is "ordered to proceed,” but official seals, or looks, or fastenings of foreign authorities are, in no case or on any pretext, to be broken, or parcels covered by them read by any naval authorities, but all bags or other things covering such parcels and dnly sealed and fastened by foreign authorities will be, in the discretion of the United States officer to whom they may come, delivered to the consul, commanding naval officer, or legation of the foreign government, to be opened upon the understanding that whatever is contraband or important as evidence concerning the character of a captured vessel will be remitted to the prize court, or to the Secretary of State at Washington, or such sealed bag or parcels may be at once forwarded to this Department, to the end that the proper authorities of the foreign government may receive the same without delay.
You are specially informed that the fact that a suspicious vessel has been indicated to you as cruising in any limit which has been prescribed by this Department does not in any way authorize you to depart from the practice of the rules of visitation, search, and capture prescribed by the law of nations.
Very respectfully,
GIDEON WELLES,
Secretary of the Navy.
O.R. of the Union and Confederate Navies,Series 1, volume 7, pp. 656-657 United States.