HMS Mersey was a Humber-class

Humber class monitor

The Humber class monitors were three large gunboats under construction for the Brazilian Navy in Britain in 1913. Designed for service on the Amazon River, the ships were of shallow draft and heavy armament and were ideally suited to inshore, riverine and coastal work but flawed for service at sea,...

 monitor of the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

. Originally built by Vickers

Vickers

Vickers was a famous name in British engineering that existed through many companies from 1828 until 1999.-Early history:Vickers was formed in Sheffield as a steel foundry by the miller Edward Vickers and his father-in-law George Naylor in 1828. Naylor was a partner in the foundry Naylor &...

 for Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 and christened Madeira, she was purchased by the Royal Navy in 1914 on the outbreak of World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 along with her sister ships Humber

HMS Humber (1914)

HMS Humber was a Humber-class monitor of the Royal Navy. Originally built by Vickers for Brazil as the Javary, she was purchased by the Royal Navy in 1914 on the outbreak of the First World War along with her sister ships and ....

 and Severn

HMS Severn (1914)

HMS Severn was a Humber-class monitor of the Royal Navy. Originally built by Vickers for Brazil, she was purchased by the Royal Navy in 1914 on the outbreak of World War I along with her sister ships Humber and Mersey. She had been christened Solimoes by the Brazilians, but was renamed by the British...

.

She had a relatively successful career in World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 and had two prominent incidents. At the Battle of the Yser

Battle of the Yser

The Battle of the Yser secured part of the coastline of Belgium for the allies in the "Race to the Sea" after the first three months of World War I.-Strategic Context:As part of the execution of the Schlieffen Plan, Belgium had been invaded by Germany...

 in 1914, off the coast of Belgium

Belgium

Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

, she bombarded German troops as well as artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 positions. In July 1915 she was towed to the Rufiji River

Rufiji River

The Rufiji River lies entirely within the African nation of Tanzania. The river is formed by the convergence of the Kilombero and Luwegu rivers. It is approximately 600 km long, with its source in southwestern Tanzania and its mouth on the Indian Ocean at a point between Mafia Island called Mafia...

 delta in German East Africa

German East Africa

German East Africa was a German colony in East Africa, which included what are now :Burundi, :Rwanda and Tanganyika . Its area was , nearly three times the size of Germany today....

 where she and Severn

HMS Severn (1914)

HMS Severn was a Humber-class monitor of the Royal Navy. Originally built by Vickers for Brazil, she was purchased by the Royal Navy in 1914 on the outbreak of World War I along with her sister ships Humber and Mersey. She had been christened Solimoes by the Brazilians, but was renamed by the British...

 then assisted in the destruction of the Kaiserliche Marine

Kaiserliche Marine

The Imperial German Navy was the German Navy created at the time of the formation of the German Empire. It existed between 1871 and 1919, growing out of the small Prussian Navy and Norddeutsche Bundesmarine, which primarily had the mission of coastal defense. Kaiser Wilhelm II greatly expanded...

 cruiser

Cruiser

A cruiser is a type of warship. The term has been in use for several hundreds of years, and has had different meanings throughout this period...

 Königsberg.

She later went to the Mediterranean and served on the River Danube

Danube

The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....

. In 1921 she was sold to the breakers.

Battle honours

• Battle of the Yser
  Battle of the Yser
  The Battle of the Yser secured part of the coastline of Belgium for the allies in the "Race to the Sea" after the first three months of World War I.-Strategic Context:As part of the execution of the Schlieffen Plan, Belgium had been invaded by Germany...
  
   1914–1915
• SMS Königsberg 1915