Pembroke Dock (Paterchurch before 1800) was the site of the only Royal Dockyard in Wales. It was the site where over 260 ships and five Royal yachts were constructed. The Admiralty closed the dock in 1926. The site was then transferred from the Admiralty to the Air Ministry in 1930 and the sheltered waters around the Haven became the home of the flying boat Squadron No. 210. Affectionately known as 'P.D.', the Royal Air Force station grew to become the largest operational flying-boat base in the world with over 100 aircraft. By far the most famous of the aircraft flown from P.D. was the Short Sunderland, a familiar sight over the skies of North and South Pembrokeshire alike.

Squadrons present during the life of the base, which closed in 1959, included air crews from Canada, Australia and New Zealand. A variety of flying boats were stationed in P.D. but the mainstay of the war years was the Sunderland; a reliable plane and with such a long range, it played a vital role in safe-guarding Atlantic Convoys and sinking German U-boats. During the Second World War, German military intelligence placed a high importance on P.D. as a military target.

The town and dockyard were subject to heavy bombing, in 1940 oil storage tanks at Pennar blazed for 18 days. In other raids the towns came out worse, with nearly 200 houses being totally destroyed.