[3]: 140 Lees served with distinction in an administrative capacity in the British Army in Germany under the command of the Marquis of Granby during the Seven Years' War.

He was employed in 1767 as a secretary by The Marquess Townshend when the latter was appointed Lord Lieutenant of Ireland and continued in the same post for his successor, the first Earl Harcourt.

[6]: 34 Their control was mainly due to the system whereby they were accountable only to the joint Postmasters General of Ireland, who being nobles were infrequently involved in the day-to-day running of the organisation.

[13][14] The building was described thus in 1825 by his eldest brother Harcourt Lees: It stands in a beautiful situation at the upper end of the town.

There is something heavy however in the external appearance of the place, the lofty gates lined with sheet iron, trebly barred and closed at all hours indicating something like fear or uneasiness in the mind of the man who deems them necessary.

[3]: 140 In 1785 when the balloonist Richard Crosbie flew from the Duke of Leinster's lawn he came down in the sea and when rescued by the Dunleary barge was landed at Blackrock House.

They were carrying troops bound for the Napoleonic war and were caught in gale-force winds and heavy snow after leaving Dublin Port.

Later a longboat was launched with the master, the captain Robert Jones, seamen and passengers when the ship was wrecked off Sir John's house.

Thirty-seven troops from the packet boat Prince of Wales were drowned nearby and it has been suggested the men may have been deliberately locked below deck while the ship's captain and crew escaped.