In his eleventh year he was sent to school at Southampton, and his education was concluded by his being placed for a twelvemonth under a French Protestant clergyman at Rotterdam, for the purpose of learning the French language.

His eldest brother, John, a lieutenant in the 8th, the King's, regiment, being promoted to a company by purchase, Isaac succeeded, also by purchase, to the ensigncy which consequently became vacant in that regiment, and to which he was appointed on the 2d of March, 1785, soon after he had completed his fifteenth year.

He joined in England, and was quartered there in different places for a few years.
Having entered the army at so early an age, he happily felt sensible of his deficiencies of education, and for a long period he devoted his leisure mornings to study, locking the door of his room until one o'clock, to prevent intrusion.

In 1790 he was promoted to a lieutenantcy, and was quartered in Guernsey and Jersey.

At the close of that year he obtained an independent company, by raising the requisite number of men to complete it, and was put on half pay.