HMS Union was a 90-gun second rate ship of the line

Ship of the line

A ship of the line was a type of naval warship constructed from the 17th through the mid-19th century to take part in the naval tactic known as the line of battle, in which two columns of opposing warships would manoeuvre to bring the greatest weight of broadside guns to bear...

 of the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

, built at Chatham Dockyard

Chatham Dockyard

Chatham Dockyard, located on the River Medway and of which two-thirds is in Gillingham and one third in Chatham, Kent, England, came into existence at the time when, following the Reformation, relations with the Catholic countries of Europe had worsened, leading to a requirement for additional...

 to the draught specified by the 1745 Establishment

1745 Establishment

The 1745 Establishment was the third and final formal establishment of dimensions for ships to be built for the Royal Navy. It completely superseded the previous 1719 Establishment, which had subsequently been modified in 1733 and again in 1741...

 as amended in 1750, and launched on 25 September 1756.

In 1756, one of the midshipmen on the Union was John Hunter

John Hunter (New South Wales)

Vice-Admiral John Hunter, RN was a British naval officer, explorer, naturalist and colonial administrator who succeeded Arthur Phillip as the second governor of New South Wales, Australia from 1795 to 1800.-Overview:...

, later to become an admiral and the second Governor of New South Wales.

In 1799, Union was converted to serve as a hospital ship

Hospital ship

A hospital ship is a ship designated for primary function as a floating medical treatment facility or hospital; most are operated by the military forces of various countries, as they are intended to be used in or near war zones....

, and continued in this role until 1816, when the decision was taken to have her broken up.