When Briand remodelled his ministry in December 1916, Cochin became an Under-Secretary of State at Foreign Affairs with responsibility for the blockade. This ministerial title merely reflected the role that Cochin had been playing throughout the whole of 1916. Trade with the enemy had been prohibited in 1914, but the naval blockade of the Central Powers was impossible to maintain because of the land borders with neutral countries, most notably Holland and Switzerland. The consequent supply of goods to the Central Powers caused the French to establish a Comité de restriction des approvisionnements et du commerce avec l'ennemi (Comit´ R) in March 1915, whose chairman Cochin became in March 1916. The appointment of such a senior minister to this post shows how important the economic war was to the French, and it followed the example of Britain who had appointed Lord Robert Cecil, Minister of Blockade in February. Cochin's powers were extended in August 1916 so that he might coordinate all the measures relating to blockade.
Although Cochin retained his ministerial position in the next government, that of Alexandre Ribot, he left office in August 1917, claiming that the "Union Sacrée" no longer existed. His accounts of the blockade were published posthumously: 1914-1922: La Guerre le blocus l'union sacrée (Paris: Plon 1923), and Les Organisations de bloçus en France pendant la guerre 1914-1918 (Paris: Plon 1926).