In July 1940, the Llangibby Castle was requisitioned as troop transport after a voyage from Capetown to Falmouth and carried troops to South and East Africa. In the night on 21/22 Dec, 1940, the ship was damaged during an air raid in Liverpool.

On 9 Nov, 1942, the Llangibby Castle was part of the KMF-convoy in the Operation Torch, the landing in North Africa. She was hit by an 8in shell from a Vichy-French shore battery which killed one person. In 1943 the ship returned to the UK for repairs to her bow, which had been damaged at Gibraltar during the preparations for the Italian landings. At the same time, she was converted into a Landing Ship Infantry (LSI) equipped with 18 landing craft and able to carry 1590 troops. After making exercises at Loch Fyne, she spent the next six months ferrying troops in the Mediterranean.
In 1944, the HMS Llangibby Castle was allotted to Force J3 (Juno beach) for the Normandy landings, based at Southampton. She practiced the landings at Bracklesham Bay. On 6 June, she landed the first wave of 750 Canadian troops at Coirseilles, loosing ten of her landing craft, which swamped on the return trip with the loss of 12 lives. The second wave of 750 men had to be landed by the remaining landing craft, which had to make two trips. After nine hours, the ship returned to Southampton. She later landed troops at the Omaha and Utah beaches and also at Le Havre, in all she made over 70 crossings and carried over 100.000 troops.
In 1945, the ship was converted back to a troop transport and carried out trooping duties in the Far East. In January 1946 she made three voyages repatriating some 6000 West African troops from Burma and India including the total internees of a military prison. In January 1947, she was returned to the owner, after having sailed 300.256 miles and carrying 156.134 troops and resumed her service after a refit. On 29 Jun, 1954, she sailed from Tilbury to Newport in Monmouthshire where she was broken up by J. Cashmore.

At 11.15 hours on 16 Jan, 1942, the Llangibby Castle (Master Bayer) in convoy WS-15 was torpedoed by U-402 north of the Azores. One torpedo hit the stern and blew away the after gun and the rudder, but the propellers remained intact. The ship limped to Horta in the Azores at 9 knots, fighting off attacks by German Fw200 aircraft on the way. The neutral Portugal allowed only 14 days for repairs and on 2 February, the ship had to left with the troops still on board and set course to Gibraltar, assisted by an Admiralty tug and escorted by three British destroyers.
On 3 February, the small convoy was followed by several U-boats, but none managed to hit the ship, while the HMS Westcott (D 47) sank U-581 (Pfeifer). On 8 February, the troopship arrived at Gibraltar in tow of the tug and disembarked the troops.

On 6 April, the Llangibby Castle left Gibraltar under escort after temporary repairs, but still without rudder, for the UK, arriving on 13 April. Altogether she sailed 3400 miles without a rudder and with a badly damaged stern, only using her engines for steering, a feat for which her master was awarded the OBE.