[2] His eldest son by his second wife, Frances, William, the 2nd baronet was a cavalry officer who committed suicide in Lisbon, Portugal in 1813 after a mental breakdown.

Erskine performed exceptionally on the field at the Battle of Emsdorf and was able to present King George III with 16 colors captured by his regiment.

Erskine was posted to America in 1776 as a brigadier staff officer under Clinton, seeing action in the New York campaign and commanding the 7th Brigade at Long Island 27 August 1776.

Erskine is credited with advising Cornwallis on the occasion of the Battle of the Assunpink Creek (also known as 'Five Mile Run') not to put off attacking the Continental Army on the night of 2 January 1777.

Erskine served in the Philadelphia campaign and then, following Sir William Howe's resignation in 1778, continued as quartermaster-general under Henry Clinton.

Erskine's last active duty in North America was commanding five infantry battalions and a cavalry squadron in pursuit of the Continental Army which was thought to be moving to Virginia in November 1778.