The Town class was a group of twenty-one light cruisers built for the Royal Navy (RN) and Royal Australian Navy (RAN) of the first half of the 20th century. These vessels were long-range cruisers, suitable for patrolling the vast expanse covered by the British Empire. These ships, initially rated as second class cruisers, were built to a series of designs, known as the Bristol (five ships), Weymouth (four ships), Chatham (three RN ships, plus three RAN ships), Birmingham (three ships, plus one similar RAN ship) and Birkenhead (two ships) classes – all having the names of British towns except for the RAN ships, which were named after Australian cities.

In 1911, the system for classifying cruisers changed such that ships over 6,000 tons were simply 'cruisers'. This would have included armored cruisers and 1st class protected cruiser. The smaller protected cruisers, scout cruisers, and the new Towns were to be 'light cruisers'. Effectively then, the Weymouths were the first Royal Navy ships built as light cruisersMorris, p.120

Design Bristol subclass

The Bristols were all ordered under the 1908–09 Programme and commissioned in late 1910.Lyon Warship Vol. 1 No. 3, p. 50. They were second class cruisers suitable for a variety of roles including both trade protection and fleet duties.Preston 1985, p. 51. They were long overall, with a beam of and a draught of . Displacement was normal and full load. Twelve Yarrow three-drum boilers fed steam turbines rated at , giving a speed of . One ship, Bristol, had Brown-Curtis turbines driving two propeller shafts, while the remaining three ships used Parsons turbines driving four shafts. Speed during sea trials varied between (Glasgow) and (Bristol).Lyon Warship Vol. 1 No. 2, p. 60. The experimental two-shaft layout of Bristol was successful, giving greater efficiency, especially at lower speeds.Lyon Warship Vol. 1 No. 2, p. 59. The ships used both coal and oil for fuel, with 1353 tons of coal and 260 tons of oil carried,Moore 1990, p. 61. giving an endurance of about at .

The Bristols were protected cruisers, with an armoured deck providing protection for the ships' vitals. The armoured deck was thick over the magazines and machinery, over the steering gear and elsewhere. The conning tower was protected by of armour, with the gun shields having armour, as did the ammunition hoists. As the protective deck was at waterline, the ships were given a large metacentric height so that they would remain stable in the event of flooding above the armoured deck. This, however, resulted in the ships rolling badly, making them poor gun platforms.Brown 2010, p. 63. One problem with the armour of the Bristols which was shared with the other Town-class ships was the sizable gap between the bottom of the gun shields and the deck, which allowed shell splinters to pass through the gap, leading to large numbers of leg injuries in the ships' gun crews.Lyon Warship Vol. 1 No. 2, p. 57.Brown 2010, p. 160.

It was originally intended that the Bristols would be fitted with a main gun armament of unshielded guns, but the need to counter German light cruisers (such as the ), which were armed with ten guns that outranged British 4-inch guns, resulted in the new class's armament being revised. They had two BL 6-inch (152 mm) Mk XI naval guns mounted on the ships' centreline fore and aft, with ten BL 4-inch Mk VII guns in waist mountings. All these guns were fitted with shields. Four Vickers 3-pounder (47 mm) saluting guns were fitted, while two submerged 18 inch (450 mm) torpedo tubes were fitted, with seven torpedoes carried.Lyon Warship Vol. 1 No. 2, pp. 55, 57. This armament was considered rather too light for ships of this size,Lyon Warship Vol. 1 No. 1, p. 53. while the waist guns were subject to immersion in a high sea, making them difficult to work.

They had a crew of 480 officers and men, with the officers accommodated in the forward part of the ship, rather than aft as per tradition, following the instructions of Admiral Fisher to improve fighting efficiency. This arrangement was unpopular, however, as it was preferred to keep officer's and other ranks accommodation separate for disciplinary reasons, while the Bristols were very cramped, with only for each seaman to live, eat, and sleep.Lyon Warship Vol. 1 No. 2, p. 61.Brown 2009, p. 59. In the First World War, the class's anti-aircraft armament was increased with the fitting of a single QF 3 inch (76 mm) 20 cwt gun.

Weymouth subclass The Weymouth subclass were ordered under the 1909–1910 Programme and commissioned between 1911 and 1912. Major changes from the Bristol subclass included a heavier main armament of eight 6 in guns, and changes to improve seaworthiness and reduce overcrowding. They were long overall, with a beam of and a draught of . Displacement was normal and full load. Machinery was similar to the Bristol subclass, with again a single example (Yarmouth) having the Brown-Curtis turbines and two-shaft arrangement used in the Bristols, while the remaining three ships had the four-shaft, Yarrow turbine machinery. Speed remained 25 knots.Preston 1985, p. 52.

Armour remained unchanged from the Bristols,Lyon Warship Vol. 1 No. 2, p. 59. while the main gun armament was changed to eight BL 6 inch Mk XI guns. The arrangement of the armament was revised, with three guns (one on the centreline and two on the beam) on an enlarged forecastle that also provided accommodation for the ships' officers. The remaining waist guns were protected by a bulwark to make them more weather resistant. Torpedo armament was increased, with two 21-inch (533 mm) submerged tubes (with seven torpedoes carried), while the ships' armament was completed by four 3-pounder saluting guns.

The Weymouths saw a number of alterations during the war, including the addition of a single 3 in (76 mm) AA gun in 1915, while the surviving ships were fitted with director control equipment for the ships' guns on a new tripod foremast. In 1917, Yarmouth was the first light cruiser to be able to operate aircraft, being fitted with a ramp above the conning tower and forecastle gun to allow a Sopwith Pup to be launched from the ship, although the aircraft could not land back on it so the pilot would have to ditch into the sea if it was not possible to reach land.Jones 1931, pp. 24–26. In 1918, Weymouth also received a similar installation.

Chatham subclass

The Chatham subclass of six ships, three for the Royal Navy and three for Australia (of which one was to be built in Australia) were ordered under the 1910–1911 Programme. The five British-built ships commissioned between 1912 and 1913, while Brisbane, the Australian-built ship was laid down in 1913 and completed in 1916. The major difference between the Chathams and the earlier Towns was a revised armour scheme. While the earlier ships were protected cruisers, depending on an armoured deck deep within the ship to protect machinery and magazines, the Chathams relied on a vertical belt of armour.Preston 1985, p. 53.

The Chathams were long overall, with a beam of and a draught of . Displacement was normal and full load. The belt consisted of of nickel-steel on top of of high-tensile steel, tapering from forward and to aft. It covered from above the waterline to below it. This belt was part of the load bearing structure of the ship, reducing the overall weight of structure required. A thin armoured deck, over most of its length and over the steering gear, was retained, mainly as a watertight deck. The ships' forecastle was again extended aft, reaching two-thirds of the length of the ship, and allowing two more guns to be raised up onto the forecastle, while the ships' metacentric height was reduced, making the ships better gun platforms.Brown 2009, p. 64. Officer's accommodation was moved back to the rear of the ships in this class. Machinery layout was again similar to the earlier Towns, with one ship, Southampton, having a two-shaft layout. It was rated at giving a speed of .

While main armament again consisted of eight 6 in guns in single mountings, a new gun, the BL 6 inch Mk XII was used. This was shorter and lighter than the Mk XI guns used in earlier ships, and while range was slightly less ( compared to ), they were much easier to handle in rough weather and were more accurate. They had larger magazines, giving up to 200 rounds per gun rather than 150 in earlier ships. The remaining armament was unchanged.

Wartime changes were similar to those made to the Weymouths, with a 3-inch anti-aircraft gun fitted during 1915 and director control with its associated tripod mast fitted later in the war. Four of the ships (Dublin, Southampton, Melbourne and Sydney) were fitted for platforms for operating aircraft.Preston 1985, p. 54.

Birmingham subclass

The 1911–1912 Programme brought the Birmingham subclass. Three ships were ordered for the Royal Navy, commissioning in 1914. A fourth, similar, ship, Adelaide, was built in Sydney for Australia. The First World War caused the construction of Adelaide, which was reliant on materials and parts from the United Kingdom, to be heavily delayed, with Adelaide not completing until 1922.Whitley 1999, p. 15. They were closely based on the Chatham subclass but with a revised armament. While in theory, three guns could fire forwards in the previous arrangement (the forward centreline gun and the forward two waist guns), in practice the effects of blast from the waist guns on the bridge and conning tower prevented this. The solution was to mount two guns side-by side on the forecastle, forward of the bridge, giving a total armament of nine BL 6 inch Mk XII guns. The remainder of the armament was unchanged (i.e. four 3-pounder saluting guns and two submerged 21-inch torpedo tubes).

The ships were long overall (Adelaide was long), with a beam of and a draught of . They displaced normal and deep load (Adelaide displaced normal and deep load). The ships' forecastle had increased flare to reduce spray. The ships' machinery was rated at giving a speed of .

A 3-inch anti-aircraft gun was fitted in 1915, while Lowestoft and Birmingham were fitted with director control. (Nottingham was lost before it could be fitted). Adelaide was completed with these modifications, and received a major refit in the 1930s, with coal-fired boilers being removed along with a funnel, reducing the ship's speed, while one 6-inch was removed, with 4-inch anti-aircraft guns added. She was subject to further armament revisions during the Second World War, with more 6- and 4-inch guns removed to accommodate depth charge throwers, and radar being fitted.

Further developments: Atlantic cruisers and Hawkins class

In 1912, work began on a new cruiser for trade protection duties in response to rumours of large German cruisers that were thought to being built for commerce raiding. A series of designs were drawn up for what became known as the "Atlantic cruiser", featuring various combinations of 7.5-inch (190 mm) and 6-inch guns, mixed oil- and coal-fired boilers and speeds of between and . When the rumoured German ships proved to be false, the Atlantic cruiser was abandoned.Brown 2009, pp. 66–67.

In 1915, as a response to German commerce raiding in the early months of the war, the British Admiralty decided to build a new class of large, fast and heavily armed cruisers for trade protection work. Again, a mixed armament of 7.5 in and 6 in guns were chosen, with mixed oil- and coal-fired boilers in order to aid operations in distant waters where oil supplies would be limited. The new design became known as the "Improved Birmingham" class or , with five being built, completing between 1918 and 1925.Brown 2009, p. 67.Preston 1985, p. 63. Later, with the advent of the 1930 London Naval Treaty, the class would become the Royal Navy's first heavy cruisers.

Birkenhead subclass