The 45th Battalion was raised in Egypt on 2 March 1916 as part of the "doubling" of the AIF. Approximately half of its new recruits were Gallipoli veterans from the 13th Battalion, and the other half, fresh reinforcements from Australia. Reflecting the composition of the 13th, the new battalion was composed mostly of men from New South Wales.

As part of the 12th Brigade of the 4th Australian Division, the 45th Battalion arrived in France on 8 June 1916, destined for the Western Front. It fought in its first major battle at Pozieres in August, defending ground previously captured by the 2nd Australian Division. After Pozieres the battalion spent the period until March 1917 alternating between duty in the trenches and training and rest behind the lines, first around Ypres in Belgium, and then in the Somme Valley in France.

The 45th Battalion was in reserve for the 4th Division's first major action of 1917 'the first battle of Bullecourt' and was not committed to the attack. It was, however, heavily engaged during the battle of Messines in June, and suffered commensurate casualties. The focus of the AIF's operations had now switched to the Ypres sector in Belgium and the 45th took part in another major battle near Passchendaele on October 12. Conditions were horrendous and the operation was hastily planned - thus it resulted in failure.

Like most AIF battalions, the 45th rotated in and out of the front line throughout the winter of 1917-18. In the spring of 1918 it played a crucial role in turning the last great German offensive of the war when it defeated attacks aimed at breaking through the British front around Dernancourt. The Allies launched their own offensive on 8 August with the battle of Amiens. On the first day of this battle the 45th Battalion captured 400 German prisoners, 30 artillery pieces and 18 machine guns. 8 August became known as the "black day of the German Army" and initiated a retreat back to the formidable defensive barrier known as the Hindenburg Line. The 45th Battalion fought its last major action of the war on 18 September 1918 around Le Verguier to seize the "outpost line" that guarded the approaches to the main defences. The battalion was out of the line when the war ended on 11 November, and was disbanded on 2 May 1919.

References
  • J.E. Lee, The Chronicle of the 45th Battalion, (Sydney: Australian Defence League, 1926).
  • AWM4/23/62/1-23/62/38
Conflict First World War, 1914-1918
Related events
Battle honours
Commanding officers
Decorations
  • 4 DSO, 1 bar; 1 OBE; 28 MC, 1 bar; 14 DCM; 140 MM, 7 bars; 6 MSM; 37 MID; 5 foreign awards
Alternative names
  • 12th Bde (45th Bn)
  • 12th LTM Bty (45th Bn)
  • 12th MGC (45th Bn)
  • 45 Battalion
  • 45 Bn
  • 45 Infantry Battalion
  • 45th Battalion (Infantry)
  • 45th Bn
  • Australian Army Medical Corps Attached 45th Battalion