WW1 War medal in great condition blackened by never being polished.

Private Sanderson was almost certainly James W. Sanderson, a Royal Scots private of the 1st Garrison Battalion who died at Gallipoli on 28 December 1915 and is buried at Lancashire Landing Cemetery; his battalion was there as a labour and guard unit supporting the Allied land campaign whose larger purpose was to force the Dardanelles and knock the Ottoman Empire out of the war.[researchingww1 +3]
Private James W. Sanderson
The Imperial War Museum “Lives of the First World War” entry records a James W. Sanderson serving with the Royal Scots, dying on 28 December 1915 and being buried at Lancashire Landing Cemetery, Gallipoli, which matches your details (name, regiment, date of death, cemetery).[livesofthefirstworldwar.iwm]
• A detailed grave list for Lancashire Landing shows “SANDERSON J W, Private 28213, Royal Scots, 28/12/1915, grave J.60,” which ties your medal naming and service number directly to that grave.[inmemories]
Private James W. Sanderson, no. 28213, Royal Scots, who died at Cape Helles while serving with the 1st Garrison Battalion and now lies in plot J.60 at Lancashire Landing.[researchingww1 +1]
1st Garrison Battalion, Royal Scots
• The 1st Garrison Battalion, Royal Scots, was formed at Redford Camp near Edinburgh on 11 August 1915, largely from drafts taken from other Scottish units and commanded from 18 August by Colonel Frederick John Brown, an experienced retired regular officer.
• Garrison battalions were intended for line-of-communication and guard duties: typically older soldiers or those not fully fit for front-line infantry service, used to guard prisoners, man defences and perform labouring work in rear areas.[researchingww1]
• After formation and basic organisation in Scotland, the battalion moved to the Eastern Mediterranean; in early November 1915 it deployed as a labour battalion to the island of Lemnos, the main British base for the Gallipoli campaign.[theroyalscots +1]
Why they were at Gallipoli
• On 8 November 1915, 10 officers and 400 selected “strongest” other ranks from the 1st Garrison Battalion were detached to Cape Helles on the Gallipoli peninsula.[researchingww1]
• Their primary task was not trench assault but heavy labour under fire: one account describes them unloading all kinds of stores from small craft onto the beaches and carrying them up the slopes to supply depots, while also furnishing guards for those dumps.[researchingww1]
• Conditions at Cape Helles in late 1915 were hazardous even for rear-area troops; these working parties operated under constant Turkish shelling, and the battalion suffered dozens of casualties from artillery fire in the weeks before the final evacuation.[researchingww1]
Given the date and place of his burial, Sanderson almost certainly fell as part of this working/guard detachment at Cape Helles during the closing phase of the campaign.[inmemories +1]