The Gorgon-class monitors were a class of monitors in service with the Royal Navy during World War I. Gorgon and her sister ship Glatton were originally built as coastal defence ships for the Royal Norwegian Navy, as HNoMS Nidaros and HNoMS Bjørgvin respectively but requisitioned for British use.

However, when World War I broke out, the Royal Navy requisitioned most warships under construction in Britain for foreign powers and refunded the two thirds of the £370,000 purchase price for each ship already paid by the Norwegians.

[2] In September 1917 work was resumed to a new design that added a large anti-torpedo bulge along about 75% of the hull's length.

[3] They were powered by two vertical triple expansion steam engines, which developed 4,000 indicated horsepower (3,000 kW) from four Yarrow watertube boilers that gave a maximum speed of 12 knots (22 km/h; 14 mph).

Addition of the bulges cost 2 knots (3.7 km/h; 2.3 mph) in speed, but prevented the extra weight resulting from all of these changes from deepening her draft.

Above it was a strake of four-inch armour that covered the area between the turrets up to the upper deck that increased to six inches abreast the wing barbettes.

The next day she bombarded another bridge; the last rounds fired by a Royal Navy warship at targets in Occupied Belgium.

[11] She was sent to Portsmouth after the end of the war where she was made available to investigate the cause of her sister ship Glatton's magazine explosion.

On the evening of 16 September Glatton's midships 6-inch magazine had a low-order explosion that ignited the cordite stored there.

Vice-Admiral Keyes ordered the destroyer Cossack to torpedo Glatton in an attempt to flood the magazine before it detonated.

[13] A Court of Enquiry held immediately afterwards found that the explosion had occurred in the midships 6-inch magazine situated between the boiler and engine rooms.

The cause was less easy to establish, but the Court noted that the stokers were in the habit of piling the red-hot clinker and ashes from the boilers against the bulkhead directly adjoining the magazine.

The magazine was well insulated with 5 inches (130 mm) of cork, covered by wood planking ¾-inch (1.9 cm) thick and provided with special cooling equipment so it was not likely that the cordite had spontaneously combusted.

The red lead paint on the bulkhead was blistered beneath the lagging and tests at the National Physical Laboratory demonstrated that it had been subject to temperatures of at least 400 °F (204 °C).

[14] As a precaution, Gorgon's cork lagging was stripped out and replaced by silicate wool which revealed the real cause.

Furthermore, a number of rivets were entirely missing which meant that ½-inch (12.7 mm) holes were present which could have dropped hot ashes onto the newspapers.

The forced draught pressure in the boiler room would have supplied air through the rivet holes which would have caused the cork to give off flammable gases and eventually ignite the cordite charges.

Work finally began in May 1925 as some 12,000 long tons (12,000 t) of silt were removed from underneath Glatton and her mainmast and superstructure were blasted away.

All the holes on her topside had to be sealed and air pumped into each compartment at a rate of 70,000 cubic feet (1,982 m3) per minute to restore her buoyancy.

The first attempt to lift her began on 2 December 1925 and was successful in breaking the suction holding her to the bottom in combination with the rising tide.