General service whistle on lanyard : Sergeant P C Callahan, 6 Battalion AIF

Standard issue police pattern nickle plated tube-bodied general service whistle with pair of opposing windows, a brass fipple and integral suspension loop. The barrel is impressed 'PATENT', while the end dome is impressed 'Patent 5727.08'. A plaited leather lanyard is tied to the loop, bearing evidence that it has broken and been re-tied on at least two occasions.

Whistle issued to and used by 1919 Sergeant (later Lieutenant ) Patrick Celestine Callahan, who was born in Victoria in 1892. A railway employee when he enlisted from Geelong, at the age of 22, on 7 January 1915, Callahan was assigned to the 5th Reinforcements of 6 Battalion, AIF. He embarked for overseas service aboard the 'Hororata' from Melbourne on 17 April, landing at Gallipoli from the 'Seang Ghoon' on 8 June. His battalion had already suffered losses at the Battle of Krithia and would suffer more in the attack on and retention of Lone Pine in early August. Callahan endured an unusually severe attack of colitis in early September, losing up to two stone (about 13 kilos) in weight , necessitating his evacuation and return to Australia; however, he was noted in Sir Ian Hamilton's Despatches of 11 December 1915. He returned to Australia aboard the Karoola from Suez on 4 November and had recovered sufficiently to return to duty at Broadmeadows on 12 June 1916. He re-embarked aboard the Euripides with 6 Battalion's 20th reinforcements, which arrived at Plymouth on 26 October 1916; Callahan reported to 2 Training Battalion, Durrington, where he was promoted to Corporal on 24 January 1917. He accompanied the reinforcements over to France on 19 June, joining 'D' Company, 6 Battalion in the field on 28 June.

His battalion had already fought at Pozières in July 1916; at Ypres, in Flanders later in the year before returning to the Somme for winter. In 1917, the battalion participated in the operations that followed-up the German withdrawal to the Hindenburg Line, and then returned to Belgium to join the great offensive launched to the east of Ypres.

Corporal Callahan was awarded the Distinguished Conduct Medal during this offensive, known as the Third Battle of Ypres. The recommendation for the award reads: 'During the operations east of YPRES at the BROODSEINDE RIDGE on 4th October, 1917, this N.C.O. showed great dash and gallantry in the attack on a crater on the Ridge. He gallantly led his Section forward and in the face of strong resistance, he first showered the post with bombs, and then rushed it and captured 17 prisoners.' Callahan was promoted to sergeant the same day. Only three weeks later, as 6 Battalion assaulted Decline Copse near Zonnebeke in stage three of the Battle of Ypres, Sergeant Callahan again distinguished himself, being recommended for and awarded the Military Medal, when, it is recorded, he 'showed great skill and resource in the reorganisation which followed on the partial destruction of one platoon on the forming-up line. .. With a small party of men he captured a machine gun and 30 prisoners'. A heavy German bombardment, presaging a German attack at precisely the same time as the Australian attack, had hit the assembling points of 1 Anzac Division, killing or wounding a seventh of the force, just prior to zero hour - these platoons Callahan reorganised. The two separate assaults met on the German side of no-man's-land, with the Australians and Scots breaking up the German attack.

After winter, Callahan was selected to attend No 14 Officer's Infantry Cadet Battalion at Catterick, until August 1918, when he qualified for a commission. One 24 September he was promoted to Second Lieutenant. He returned to France on 7 November, rejoining his battalion on 31 November. He returned to Australia on 23 September 1919. Callahan enlisted again during the Second World War, serving as a lieutenant with the number V17633, with 12 Garrison Battalion between July 1941 and April 1944.

As a sergeant and a platoon's second-in-command, Callahan would have used his whistle in action as a aid to commanding his platoon; usually only a small number of whistle blasts were used to indicate pre-designated commands - one, two or three blasts to indicate simple movements such as advance, stop or withdraw.