A sailor and labourer before World War I, he enlisted in the Australian Imperial Force (AIF) in March 1915, serving with the 10th Battalion during the latter stages of the Gallipoli campaign.

After the Australian force withdrew to Egypt, Jensen was transferred to the newly formed 50th Battalion, and sailed for France with the unit in June 1916.

On the Western Front, he was wounded during the battalion's first serious action, the Battle of Mouquet Farm in August, and only returned to his unit in late January 1917.

On 2 April, his battalion attacked the Hindenburg Outpost Line at Noreuil, where his actions leading to the capture of over fifty German soldiers resulted in the award of the Victoria Cross.

Shortly after the fighting at Villers-Bretonneux, Jensen was on patrol when he received a severe head wound, and was evacuated to the United Kingdom, then repatriated to Australia, where he was discharged in Adelaide at the end of the war.

[1][4][5] On 23 March 1915, Jensen enlisted as a private in the Australian Imperial Force (AIF) for service in World War I; he was allotted to the 6th reinforcements to the 10th Battalion.

[1][6] His reinforcement draft embarked on HMAT Borda at Outer Harbor on 23 June, and joined the battalion at Gallipoli, Turkey, on 4 August.

[8] For the remainder of the Gallipoli campaign, the 10th Battalion rotated through various positions in the line defending the beachhead until withdrawn to Lemnos in November.

[11] The battalion embarked for Egypt in late November and spent the next four months training and assisting in the defence of the Suez Canal.

The 50th Battalion continued to rotate through front line, support and reserve positions, and underwent training in rear areas.

[18] During this assault, which was preceded by a weak artillery barrage, the 50th Battalion suffered extraordinary difficulties, and the centre company, to which Jensen belonged, was forced to detach a party of men equipped with a large number of hand grenades (then known as bombs) to deal with a strongly barricaded German post that was holding out between their company and the one on their right.

[21] The recommendation read:[22] At Noreuil on 2nd April 1917, this man took charge of five men and attacked a barricade behind which were 40/50 Germans with a machine gun.

[1][16] His award of the Victoria Cross appeared in The London Gazette on 8 June,[22] by which time the 50th Battalion was involved in the Battle of Messines,[14] suffering 149 casualties.

[1][28][29] In late March 1918, the battalion left its rest area and, along with many other Australian units, was quickly deployed to meet the German spring offensive south of the River Ancre.

Following two weeks' leave, he was repatriated to Australia, along with nine other Victoria Cross recipients, in August 1918 to take part in a recruiting campaign on the invitation of Prime Minister Billy Hughes.

[35] After his discharge, Jensen worked for a short time as a barman in Truro,[36] then as a marine store dealer in Adelaide.

painted on the side, was published on the front page of The Sunday Times newspaper in Sydney; the caption noted that he employed several men in his business.