The natural harbour (now the Milford Haven Waterway) at the mouth of the River Cleddau in south west Wales offered shelter from the prevailing winds, probably for many thousands of years. A fort had been built at Pater or Paterchurch, near Pembroke Town on the southern side of the waterway in 1758 by the Ordnance Department. In 1797, at the height of the invasion threat in the Napoleonic Wars, the Government sought to buy the privately owned Milford Yard on the northern bank to establish a new naval dockyard. However by 1809, facing unreasonable demands for the purchase, it was decided instead to adopt an alternative site at Paterchurch.
John Rennie was appointed and visited the site in 1813 with the Comptroller of the Navy to determine the best scheme for the dockyard in 1813. He was heavily involved in the project for the rest of his career and his last business letter, relating to the construction of the entrance gates to Pembroke Dock, was written on 28 September 1821 just a week before he died.
Despite the threat having abated following Napoleon’s defeat at Waterloo, work continued after Rennie’s death under the resident engineer William Wallace and the contractor Hugh McIntosh. By 1825 twelve building slips had been built or planned along with all the workshops and storehouses. The name Pater was soon dropped and a hydrographic survey of Pembroke Dock in 1832 shows projected Dockyard buildings and features as well as those existing at the time according to the plan ‘proposed by the Comptroller and Mr. Rennie’’ From its opening, Pembroke Dock developed through two main periods of extension in 1830-2 and again in 1844, including the construction of timber covered slipways to Sir Robert Seppings’s designs and subsequently pioneering iron roofs by Fox Henderson in June 1845.
Pembroke Dockyard closed in 1926 but was subsequently used as a Royal Air Force flying-boat station, RAF Pembroke Dock, until 1959; a commercial ferry port and the base for the Royal Maritime Auxiliary Service until 2008 when the site was sold to the Milford Haven Port Authority. Over 260 Royal Navy vessels were launched at the dockyard up to its closure.
In 2011, the Institution of Civil Engineers Panel for Historical Engineering Works celebrated the work of John Rennie on the 250th anniversary of his birth by unveiling a plaque at Pembroke Dock on Sunderland House.