She was designed as an English Channel ferry for the South Eastern and Chatham Railway (SE&CR), who operated her between Folkestone and Boulogne.

In 1940 Mona's Isle was the first ship to complete a round trip during the Dunkirk evacuation, rescuing a total of 2,634 troops.

Her most prestigious passenger in her cross-channel service was King Edward VII, who crossed from Dover to Calais aboard her on 4 May 1905.

[7] On 1 June 1908, Onward was involved in a head-on collision with another SE&CR ferry, The Queen,[8] killing the bow lookout man.

[9] In the First World War Onward carried British Expeditionary Force troops on her regular route between Folkestone and Boulogne.

On 24 September 1918 a thermite bomb started a fire aboard Onward when she was moored alongside a pier in Folkestone Harbour.

After the war only four returned, so the company urgently needed replacement ships to resume peacetime services.

In order to meet tourist demand in 1919 the company bought the Laird Line ship Hazel and renamed her Mona.

Mona's Isle served various IoMSP routes, but mainly worked summer services linking Douglas with Belfast and Dublin.

After the Second World War began, the Admiralty requisitioned several IoMSP ships and had them converted into ocean boarding vessels (OBVs).

Toward the end of May 1940, Mona' Isle was one of eight IoMSP ships that were sent to Dunkirk to help to evacuate the British Expeditionary Force in Operation Dynamo.

[12] The shortest was "Route Z", 39 nautical miles (72 km), which went west from Dunkirk along the French coast as far as No.6 Buoy, then turned west-northwest straight to Dover.

The longest was "Route Y", 87 nautical miles (161 km), went east along the French and Belgian coast as far as Bray-Dunes then turned north-northeast until reaching the Kwinte Buoy.

Mona's Isle returned by Route Z and came under fire from German shore batteries on the French coast.

He had remained at a 12-pounder gun despite multiple wounds, and took a great risk in coming out of cover to close the cordite boxes.

Mona's Isle made a second round trip to Dunkirk, evacuating another 1,200 troops, and bringing her total to 2,634.