The M29 class of monitors was designed by Assistant Constructor Charles S. Lillicrap, in early March 1915. Each was to carry two six-inch guns, one forward and the other aft. The order for the five ships of this class was given to Harland & Wolff of Belfast on 15 March. They subcontracted the building of M32 and M33 to the nearby yard of Workman, Clark & Company.

April 1915
The keel for Monitor M33 was laid on 1 April.

May 1915
Monitors M29, M32 and M33 were launched on 22 May.

June 1915
Monitor M33 was commissioned at Belfast on 17 June. She was based at Devonport and commanded by Lt. Cmdr. Q.B. Preston–Thomas. Monitor M33 was accepted from the builders and ordered to war on 24 June.

The Dardanelles campaign, begun in February 1915, aimed to break through the Turkish defences in the Dardanelles Strait, capture Constantinople and destroy Turkey as a fighting force. To achieve control of the Strait the Gallipoli Peninsula needed to be in Allied possession. The Gallipoli landings began at the end of April. Monitor M33 and some of her sister ships arrived in the Aegean in time to help cover the landing of reinforcements along the southern coast of the Peninsula during August. However by this time the campaign was failing and by January 1916 allied troops were evacuated from the peninsula.

Some further activities of Monitor M33 during the First World War are listed below.

Animated film of M33 in action 1915

Jan 1916
Assisted the army in establishing a base at Stavros. Acted as guard ship or boom defence vessel at Salonika, the Allied base for the war in Bulgaria.

May 1916
Under enemy fire assisted in salvaging guns from the damaged M30 beached on Long Island in the Gulf of Smyrna. Covered the evacuation of the wireless telegraph station and aerodrome on Long Island.

HMS Monitor M33 at Chios, 1918
© National Media Museum/Science & Society Picture Library

July 1916
Provided covering fire during a cattle raid on the Turkish coast.

Aug 1916
Monitors M33 and M32 were detached to assist the French bombardments on the south coast of Turkey.

Dec 1916
Tasked with protecting the bridge between Euboea and mainland Greece from Greek Royalist troops.

May 1917
Bombarded enemy batteries near Suvla and Anzac Beaches on the Gallipoli Peninsula.

Nov 1918
One of the vessels supervising the armistice with Bulgaria at Stavros and with Turkey at Syra.

April 1919
Returned to England and decommissioned.

Monitor M33 was refitted and then recommissioned on 10 May 1919 and sent to North Russia with the British Relief Force to cover the withdrawal of Allied and White Russian troops.

Monitors M31, M24, M25, M26 and M27 were also part of the Relief Force. The action was known as the Dvina River Campaign.

June 1919
Arriving at Archangel in early June, the force steamed up river and bombarded Bolshevik positions including Seltso and Selemengo Wood, allowing an orderly Allied retreat.

Aug 1919
The bombardments continued into August. Throughout the campaign the river level was unusually low. On the return to Archangel at the end of August the guns had to be removed and loaded onto barges. Monitor M33 had dummy guns made from driftwood, pipes and biscuit tins to fool the enemy.

Sept 1919
On the 23rd with the guns back aboard, Monitor M33 returned upriver to Spaskoe to cover the evacuation of the last 500 British troops. Monitors M33, M31 and M26 were amongst the last to leave. Monitors M25 and 27 with their larger guns and deeper draft had run aground on the way back to Archangel. They were scuttled after having their guns removed.

Oct 1919
Monitor M33 returned to Chatham on 17 October.