HMAS Choules (L100) is a Bay-class landing ship that served with the Royal Fleet Auxiliary (RFA) from 2006 to 2011, before being purchased by the Royal Australian Navy (RAN). The vessel was built as RFA Largs Bay by Swan Hunter in Wallsend, Tyne and Wear. She was named after Largs Bay in Ayrshire, Scotland, and entered service in November 2006. During her career with the RFA, Largs Bay served as the British ship assigned to patrol the Falkland Islands in 2008, and delivered relief supplies following the 2010 Haiti earthquake.

At the end of 2010, Largs Bay was marked as one of the vessels to be removed from service under the Strategic Defence and Security Review. She was offered for sale, with the RAN announced as the successful bidder in April 2011. After modifications to make her more suited for Australian operating conditions, the vessel was commissioned in December 2011 as HMAS Choules, named after Royal Navy and Royal Australian Navy Chief Petty Officer Claude Choules. A propulsion transformer failure kept the ship out of service between July 2012 and April 2013.

The Bay class was designed as a replacement for the Round Table-class logistics ships operated by the RFA. The new design was based on the Royal Schelde Enforcer design; a joint project between the Dutch and Spanish resulting in the Rotterdam-class and Galicia-class amphibious warfare ships. The main difference with the British ships is the lack of a helicopter hangar. The ships were originally designated "auxiliary landing ship logistics" or ALSL, but this was changed in 2002 to "landing ship dock (auxiliary)" or LSD(A), better reflecting their operational role. Four ships were ordered; two from Swan Hunter, and two from BAE Systems Naval Ships.

The Bay-class ships have a full load displacement of 16,160 tonnes (15,900 long tons) in RFA service; this increased slightly to 16,190 tonnes (15,930 long tons) after modifications for RAN service. Largs Bay/Choules is 579.4 feet (176.6 m) long, with a beam of 86.6 feet (26.4 m), and a draught of 19 feet (5.8 m). Propulsion power is provided by two Wärtsilä 8L26 generators, providing 6,000 horsepower (4.5 MW), and two Wärtsilä 12V26 generators, providing 9,000 horsepower (6.7 MW). These are used to drive two steerable propulsion pods, with a bow thruster supplementing. Maximum speed is 18 knots (33 km/h; 21 mph), and the Bay-class ships can achieve a range of 8,000 nautical miles (15,000 km; 9,200 mi) at 15 knots (28 km/h; 17 mph). Largs Bay was fitted for but not with a Phalanx CIWS and a 30mm DS30B cannon when required for self defence. The RAN's webpage for Choules does not specify any armament. In British service, the everyday ship's company consisted of 60 to 70 RFA personnel, with this number supplemented by members of the British Armed Forces when Largs Bay was deployed operationally. The RAN opted to maintain the ship at full operational crewing at all times, with a ship's company of 158, including 22 Army and 6 RAAF personnel.

As a sealift ship, Largs Bay is capable of carrying up to 1,150 linear metres of vehicles; equivalent to 24 Challenger 2 tanks, 32 M1A1 Abrams tanks, or 150 light trucks. The cargo capacity is equivalent of 200 tons of ammunition, or 24 twenty-foot equivalent unit containers. During normal conditions, a Bay-class ship can carry 356 soldiers, but this can be almost doubled to 700 in overload conditions. The ship does not have permanent hangar facilities. However, a temporary hangar may be fitted and in Australian service the twin-spot flight deck has been extensively utilized with the embarkation of Blackhawk, MRH-90 and Seahawk helicopters. In the period one year prior to April 2014 the ship had clocked up 1,000 deck landings. The flight deck is capable of accommodating helicopters up to the size of a Chinook heavy-lift helicopter. The well dock can carry one LCU Mark 10, one LCM-8, or two LCVPs (either the Royal Marines version or the Royal Australian Navy version), and two Mexeflotes can be suspended from the ship's flanks. The LCM-1E landing craft being acquired by the RAN will not fit into the dock. Two 30-ton cranes are fitted between the superstructure and the flight deck.

Largs Bay and sister ship Lyme Bay were ordered from Swan Hunter on 18 December 2000. Largs Bay was laid down at Swan Hunter's shipyard at Wallsend, Tyne and Wear on 28 January 2002; the first ship of the class work started on. The ship was launched on 18 July 2003. The ship was completed and accepted by the Ministry of Defence in April 2006, over a year late. Largs Bay was dedicated on 28 November 2006, the second of the class to enter service with the RFA. The Bay-class construction project saw major delays and cost overruns, particularly in the Swan Hunter half of the project. Shortly after Largs Bay was handed over, Swan Hunter was stripped from the project, with BAE taking full responsibility for the class and Lyme Bay towed to BAE's shipyard in Govan for completion in June 2006.

Four months after entering service, an engine room fire resulted in steering and propulsion issues, requiring Largs Bay to be towed to Plymouth for repairs. In late November 2007, Largs Bay embarked 815 Naval Air Squadron 215 Flight and left home waters for the Caribbean to conduct counter-drug operations. She visited eleven islands including Barbados, Curaçao, Grand Turk, Martinique, Trinidad and also the USA. Three days after leaving Barbados Largs Bay's patrolling helicopter spotted a small fishing vessel stopped in the water and detained her after a pursuit; 575 kilograms (1,268 lb) of cocaine were recovered, with an estimated £20 million European street value. She participated in Navy Days while in port at Curaçao, where several hundred people toured her.

In late 2008, it was reported that Largs Bay was to replace HMS Northumberland for duties in the Falkland Islands. Northumberland was to have left for the Islands in December 2008, but was instead sent for pirate patrol off Somalia.