To stop treasure-ships, or to embargo merchant-ships, when difficulty was threatening, was no new idea to the British Government.

The latter had been done with Baltic merchantmen at the time of the Armed Neutrality.
In the case of Spain, it was a measure particularly efficacious, for the financial solvency and belligerent capacity of that country depended upon the galleons, which brought to her the tribute of her colonies; and her relations and dealings with France at this time were so partial and suspicious as to justify precautions.

Evidently, however, such a step, being avowedly preventive and not offensive, should be taken in such a way as to avert all chance of possible disaster.

Several Spanish frigates being expected, the British Government charged four vessels of the same rate with the task of arresting them.

Nelson, the instant he got his orders, detached to the spot an eighty-gun ship, to which he added four other cruisers, thinking, as he said in his orders to the captain selected, that "this is a service of the highest importance, and that an officer of your rank and experience should be employed therein." With such odds against him, the Spanish commander would need no military justification for submission.