The bulk of Britain's light cruisers were obsolete by 1930, and various other navies were commissioning modern 152mm-armed ships, such as the German Koenigsberg-class cruisers, with mask mounts and other recent upgrades.
Such was the background that guided the studies of the five cruisers of the Leander series:Achilles, Ajax, Leander, Neptune and Orion, with elegant and balanced lines, with a single funnel grouping two sets of smoke pipes.
The two most important features were their eight-piece 152 mm artillery and their speed of 32 knots. Their double 152 mm mounting under mask had been developed from those of the cruiser Enterprise then of the battleships Nelson and Rodney.
Unlike their contemporaries, notably the Italian cruisers armed with 152 mm, the Leanders had decent protection, which proved to be profitable when Ajax and Achilles had to face the Graf Spee. As for the Neptune, it gave a demonstration of the effectiveness of its underwater protection by staggering the explosions of four mines before sinking in the middle of a minefield in the Mediterranean.
If the Leander were excellent buildings, well balanced, they nevertheless had the defect of not having a driving and evaporating apparatus divided into two groups machines and boilers; in other words, the boilers were contiguous, so that a single impact could put them all out of service.
The plans of the following three units were rectified so that the whole the propulsion is presented in the succession boiler-machine, boiler-machine; they were called “modified Leanders”. This imposed the return to the two fireplaces of a less massive and perhaps more elegant aspect. All three were transferred to the Australian Navy, which renamed them Hobart, Perth, and Sydney.
H.M.S. AJAX
Displacement Washington , 6,985 t; at full
load , 8,950 t
Length 168.82 m overall
Width 16.98 m
Average draft , 4.87 m
Propulsion 4 shaft lines, gear turbines, 72,000 hp, 32.5 knots
Protection
cuirass belt , 50-100 mm;
bridge, 50 mm;
turrets , 25 mm
Artillery 8 pieces of 152 mm, 8 of 100 mm AA; 4 quadruple machine guns
L.T Tubes . 8 × 533 mm torpedo tubes
Launched March 1, 1934 at Vickers-Armstrong, Barrow