Cerberus-class breastwork monitor

Stern view of Cerberus at Williamstown, Victoria in 1871
Class overview
Builders:	Thames Ironworks and Shipbuilding Company Palmers Shipbuilding and Iron Company
Operators:	Royal Navy  Royal Australian Navy
Built:	1867–1870
In commission:	1870–1924
Completed:	2
General characteristics
Displacement:	3,344 long tons (3,398 t)
Length:	225 ft (69 m)
Beam:	45 ft (14 m)
Draught:	15 ft 4 in (4.67 m)
Propulsion:	2 shaft Maudslay, 1,360 ihp (Cerberus) 2 shaft Ravenhill 1,436 ihp, (Magdala)
Speed:	9.75 knots (11 mph; 18 km/h) (Cerberus) 10.6 knots (12 mph; 20 km/h) (Magdala)
Complement:	155
Armament:	4 × 10-inch (254 mm) (2 × 2) Rifled Muzzle Loading guns
Armour:	Belt: 6–8 in (150–200 mm) with 9–11 in (230–280 mm) wood backing Turret: 9–10 in (230–250 mm) Breastworks: 8–9 in (200–230 mm) Deck: 1–1.5 in (25–38 mm)

The Cerberus-class breastwork monitor was a pair of breastwork monitors built for the Royal Navy in the 1860s.

Also referred to as "ironclads" and "turret ships", the ships of the Cerberus class were designed by Sir Edward Reed following requests by several dominions and colonies of the British Empire for warships to be used as coastal defence ships. The class consisted of two ships: HMS Cerberus, which was operated by the colony of Victoria, and HMS Magdala, which spent her life operating in Bombay Harbour.

The size of the ships was limited by cost. They were designed and built to be used as local defence ships, and it was not expected that they would ever need to be deployed far away from their bases. It was therefore possible to design them without sails or rigging and dependent only upon their engines, with a resulting limitation in their effective range.

The absence of masts and rigging allowed more weight to be worked into the ship's armour. This also meant it was possible to arm the ships with two gun turrets, one fore and one aft, which had wholly unobstructed fields of fire over the bow and stern, and on wide arcs amidships. The turrets were mounted on the upper deck and hence had a greater height above water and a correspondingly greater command than guns mounted on the main deck. The turret armament provided an additional advantage of allowing the ships to have a low freeboard. This increased the steadiness of the ship and allowed the hull armour to be applied more thickly over a more limited height of exposed hull.