Per his military service record (regimental no. 4748), William Cairns was born at Strawberry Hills, Sydney, N.S.W.  He gave his age as 26 years and 5 months, his marital status as married, and his occupation as laborer. His description on his Certificate of Medical Examination was height 5 feet 3 ¼ inches tall, weight 131 lbs., with a medium complexion, brown eyes, and black hair. His religious denomination was Church of England. He claimed that he had no previous military service.
He completed his medical examination on 2nd November 1915 at Lithgow (when the Coo-ees were at Lithgow), and was attested by Captain A. C. Eade at Lithgow on 2nd November 1915.
After completing the Coo-ee March he went to Liverpool Camp as reinforcement for the 13th Battalion.
On 25th November 1915 Private Cairns was charged with being absent without leave. He was fined one days pay.
On 22nd December 1915 Private Cairns was charged with being absent without leave for four days. He was fined two shillings and forfeited four days pay.
On his embarkation roll his address at time of enrolment was Farr Street, Rockdale, N.S.W., and his next of kin is listed as his wife, Mrs. A. [Alice] Cairns, 31 Junction Road, North Sydney, N.S.W.
On 8th March 1916 Private Cairns departed Sydney on the HMAT A15 Star of England, along with many of the other Coo-ees, and arrived in Egypt on 11th April 1916.
On 24th May 1916 Private Cairns was admitted to the 2nd Australian Stationary Hospital at Tel-e-Kebir, suffering from Influenza. On 26th of May 1916 he was sent to the Base Details Depot at Helopolis, Egypt.
On 2nd August 1916 Private Cairns was charged with being absent without leave from the 1700 Parade and absent from Piquet. He was awarded seven days Field Punishment Number 2.
On 6th August 1916 Private Cairns left Alexandria aboard His Majesty’s Transport Megantic bound for England, arriving at Portsmouth later that month. He then marched into the 4th Training Battalion.
On 22nd September 1916 Private Cairns left England bound for France. On 24th September 1916 he marched into the 4th Australian Division Base Depot at Etaples, France.
He was taken on strength of the 13th Battalion on 6th October 1916 when it was manning the front line in the St Eloi sector in Belgium.
On 17th October 1916 Private Cairns was sent to the 13th Australian Field Ambulance sick. On 18th October 1916 he was sent to the 4th Australian Field Ambulance, then to the Division Rest Station. On 25th October he was moved to the 1st Convalescent Depot at Boulogne, France. On 26th October 1916 he was admitted to the 18th General Hospital at Camiers, France.
On 23rd November 1916 he was transferred to the 51st General Hospital at Etaples, France.
On the 5th of December 1916 he was discharged and sent to the 4th Australian Division Base Depot also at Etaples, France.
On 8th December 1916 Private Cairns was charged with Drunkenness and being in possession of spirits on 6th December 1916. He was awarded 28 days Field Punishment Number One.
On 23rd December 1916 Private Cairns rejoined the 13th Battalion when it was training at Coisy, France.
On 28th January 1917 Private Cairns was admitted to the 13th Australian Field Ambulance with eye problems. He was moved back to the Division Rest Station.
He rejoined the 13th Battalion on 2nd February 1917 when it was being relieved from the front line in the vicinity of Guedecourt, France.
On 26th February 1917 Private Cairns was charged with when on active service being in Amiens without a pass, and not complying with an order given by a Military Police officer. He was fined seven days pay.
On 13th March 1917 Private Cairns was sent to the 13th Australian Field Ambulance suffering Influenza. On 30th March 1917 he was transferred to the 5th General Hospital at Rouen, France, suffering Cystitis.
On 16th April 1917 Private Cairns was placed aboard the Hospital Ship St George at Rouen for evacuation to England. On 17th April 1917 he was admitted to the Graylingwell War Hospital at Chichester, England, with Pyrexia.
On 4th May 1917 Private Cairns was transferred to the 3rd Australian Auxiliary Hospital at Dartford, England. He was discharged on 14th May 1917, and granted leave to report to the Training Battalion at Hurdcott, England, on 29th May 1917.
On 30th May 1917 Private Cairns was moved to the 3rd Command Depot at Hurdcott, England.
On 30th June 1917 Private Cairns marched into the Overseas Training Brigade at Pernham Downs, England.
On 20th July 1917 Private Cairns was admitted sick to the 1st Australian Dermatological Hospital at Bulford, England. He was discharged on 24th July 1917, and sent to the Convalescent Training Depot.
On 6th September 1917 Private Cairns was transferred to the Number 1 Command Depot at Perham Downs, England.
On 18th October 1917 Private Cairns was charged with being absent without leave from 1400 on 2nd October 1917 till being apprehended by the Military Police at 1100 on 15th October 1917, and losing by neglect his pass. He was awarded Field Punishment Number Two and fined 28 days pay.
On 23rd October 1917 Private Cairns marched into the Overseas Training Brigade at Longbridge Deverell, England.
On 3rd November 1917 Private Cairns was admitted to the Sutton Veny Hospital suffering Trachoma. A Medical Report of an Invalid form dated 3rd November 1917 in his file recorded that the disability dated from 4th February 1917 at Fleurs, France, where ‘phosphorus from shells caused irritation of eyes which gradually became worse’.
On 9th November 1917 he was transferred to the 1st Australian Auxiliary Hospital at Harefield, England.
On 6th December 1917 Private Cairns was charged with being absent without leave from the 1st Australian Auxiliary Hospital from 2045 on 4th December 1917 till 8.45pm on 5th December 1917. He was fined three days pay.
On 14th December 1917 Private Cairns was discharged from hospital and sent to the Number 2 Command Depot at Weymouth, England.
Private Cairns left England on the H.M.A.T. Runic on 20th December 1917, for return to Australia, suffering Trachoma. He disembarked at Sydney on 14th February 1918.
Private Cairns was discharged Medically Unfit on 13th August 1918.
Note: William Cairns died the year after he returned to Australia, at the No 4 Australian General Hospital (Randwick Military Hospital), on 2nd April 1919. He was buried at Gore Hill Cemetery at Gore Hill, Sydney. His name is remembered on the Australian War Memorial Roll of Honour.
 NAA: B2455, CAIRNS W
 Australian War Memorial Roll of Honour, William Cairns, https://www.awm.gov.au/people/rolls/R1677339/