Subsidiary to this main effort, Napoleon also contemplated a simultaneous landing of some twenty thousand men in Ireland, which, like the naval movements, would distract and tend to divide the unity of the British resistance.

The British admirals considered this project to be easier than the invasion of Great Britain, and it engaged their much more serious attention.
There were three principal French detachments to be united,--in Brest twenty ships, in Toulon ten, in Rochefort five.

To these the outbreak of the war between Great Britain and Spain added the forces of the latter kingdom, in Ferrol and Cadiz, aggregating fifteen serviceable ships; but this was not until March, 1805.

Of the three French contingents, the one from Rochefort was small; and, as a factor, although important, it was not essential.

Its failure might weaken or impede the progress of the general movement, without entirely destroying it; but it was of necessity that the Toulon and Brest divisions both should fulfil their missions, accurately and on time, if the great combination, of which they were parts, was to advance to a triumphant conclusion.