With a party of 100 reinforcements from Canada and 350 of his own men, this campaign resulted in the temporary capture of Bay Bulls and Petty Harbour in January 1705 and a failed siege of the main English settlement at St. John's.

He successfully led the outnumbered defense of Port Royal against two failed sieges in 1707, leading several sallies himself and having his own horse killed under him in one skirmish.

The governor of Boston was not prepared to accept defeat and on 5 October 1710 General Francis Nicholson's fleet appeared before Port-Royal and began the Siege of Port Royal.

After a few days of defense, Subercase surrendered the partially ruined and under-provisioned Port-Royal to the British, expressing to the English commander his hope of returning to pay him a visit the following spring.

Subercase, accused of negligence by some officers and reprimanded by New France governor Vaudreuil, was summoned before a court-martial at Rochefort, but rapidly acquitted.

In 1711 he was presented an offer to serve in Quebec under Vaudreuil, where he could formulate a plan to retake Port-Royal, while continuing to receive his salary as governor of Acadia.