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.
His reinforcement draft embarked on HMAT Borda at Outer Harbor on 23 June, and joined the battalion at Gallipoli, Turkey, on 4 August.
By the time Jensen arrived, nearly half of the battalion had been evacuated sick with dysentery.
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the Gallipoli campaign, the 10th Battalion rotated through various positions in the line defending the beachhead until withdrawn to Lemnos in November.
Jensen remained with his unit throughout, except for a week in September–October that he spent in hospital.
The battalion embarked for Egypt in late November and spent the next four months training and assisting in the defence of the Suez Canal.
While in Egypt, the battalion was split into two, one half forming the nucleus of the new 50th Battalion, which was part of the 13th Brigade, 4th Division.
In April 1916, Jensen and several other 10th Battalion men were transferred to the 50th Battalion; later that month Jensen was charged for not being in his tent at tattoo.
On 5 June the battalion embarked for France, arriving in Marseilles six days later.
The unit then entrained for the Western Front, entering the trenches for the first time on 28 June near Fleurbaix.

The 50th Battalion saw its first serious action during the Battle of Mouquet Farm in mid-August 1916.
During the battle, the 50th Battalion suffered 414 casualties, largely from the heavy German artillery bombardment.
On 14 August, Jensen was hit in the left shoulder by a piece of shrapnel.
He was evacuated to the UK and admitted to Graylingwell War Hospital in Chichester, West Sussex.
While in the UK, he was charged with more disciplinary infractions in September, December and January, on one occasion being sentenced to 28 days field punishment for missing the troop train to return to France, and on another serving 12 days detention for being absent without leave.
He did not rejoin his unit until 28 January 1917.


The 50th Battalion continued to rotate through front line, support and reserve positions, and underwent training in rear areas.
The battalion was also involved in pursuing the Germans as they withdrew to the Hindenburg Line of fortifications.
On 2 April, the 13th Brigade attacked the Hindenburg Outpost Line at Noreuil.
The attack consisted of the 51st Battalion attacking the village from the north, and the 50th Battalion from the south.
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.
Jensen was a member of this party.
His actions during the reduction of this post resulted in a recommendation for the Victoria Cross, the highest award for gallantry in battle that could be awarded to a member of the Australian armed forces at that time.
He was assisted in his actions by Private William Quinlan O'Connor and four others.
The recommendation read: 
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.
One of his men shot down the German gunner.
Jensen who is a Dane, then rushed the whole post singlehanded and threw a bomb in.
He had still a bomb in one hand and taking another from his pocket he drew the pin with his teeth.
Threatening them with two bombs, he called on them in German to surrender and bluffed them that they were surrounded by Australians.
The enemy dropped their rifles and gave in.
Jensen then sent a German to tell another enemy party who were fighting our Stokes Gun to surrender and they too gave in.
A different party of our men then saw these Germans for the first time and began firing on them.
At considerable risk, Jensen stood up on the barr
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. His reinforcement draft embarked on HMAT Borda at Outer Harbor on 23 June, and joined the battalion at Gallipoli, Turkey, on 4 August. By the time Jensen arrived, nearly half of the battalion had been evacuated sick with dysentery. 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. Jensen remained with his unit throughout, except for a week in September–October that he spent in hospital. The battalion embarked for Egypt in late November and spent the next four months training and assisting in the defence of the Suez Canal. While in Egypt, the battalion was split into two, one half forming the nucleus of the new 50th Battalion, which was part of the 13th Brigade, 4th Division. In April 1916, Jensen and several other 10th Battalion men were transferred to the 50th Battalion; later that month Jensen was charged for not being in his tent at tattoo. On 5 June the battalion embarked for France, arriving in Marseilles six days later. The unit then entrained for the Western Front, entering the trenches for the first time on 28 June near Fleurbaix.
The 50th Battalion saw its first serious action during the Battle of Mouquet Farm in mid-August 1916. During the battle, the 50th Battalion suffered 414 casualties, largely from the heavy German artillery bombardment. On 14 August, Jensen was hit in the left shoulder by a piece of shrapnel. He was evacuated to the UK and admitted to Graylingwell War Hospital in Chichester, West Sussex. While in the UK, he was charged with more disciplinary infractions in September, December and January, on one occasion being sentenced to 28 days field punishment for missing the troop train to return to France, and on another serving 12 days detention for being absent without leave. He did not rejoin his unit until 28 January 1917.

The 50th Battalion continued to rotate through front line, support and reserve positions, and underwent training in rear areas. The battalion was also involved in pursuing the Germans as they withdrew to the Hindenburg Line of fortifications. On 2 April, the 13th Brigade attacked the Hindenburg Outpost Line at Noreuil. The attack consisted of the 51st Battalion attacking the village from the north, and the 50th Battalion from the south. 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. Jensen was a member of this party. His actions during the reduction of this post resulted in a recommendation for the Victoria Cross, the highest award for gallantry in battle that could be awarded to a member of the Australian armed forces at that time. He was assisted in his actions by Private William Quinlan O'Connor and four others. The recommendation read: 
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. One of his men shot down the German gunner. Jensen who is a Dane, then rushed the whole post singlehanded and threw a bomb in. He had still a bomb in one hand and taking another from his pocket he drew the pin with his teeth. Threatening them with two bombs, he called on them in German to surrender and bluffed them that they were surrounded by Australians. The enemy dropped their rifles and gave in. Jensen then sent a German to tell another enemy party who were fighting our Stokes Gun to surrender and they too gave in. A different party of our men then saw these Germans for the first time and began firing on them. At considerable risk, Jensen stood up on the barr
Jørgen Jensen (soldier)