Question: When did the battle occur for which William Johnstone Milne received the Victoria Cross?

Context articles: Battle of Vimy Ridge
Victoria Cross (Canada)
William Johnstone Milne
List of Irish Victoria Cross recipients
William Johnstone, 1st Marquess of Annandale
Jay Johnstone
William Johnstone (VC)
Steven Milne
Nellie Johnstone No. 1
List of Australian Victoria Cross recipients

The Battle of Vimy Ridge was a military engagement fought primarily as part of the Battle of Arras, in the Nord-Pas-de-Calais region of France, during the First World War.
 The main combatants were the Canadian Corps, of four divisions, against three divisions of the German Sixth Army.
 The battle, which took place from 9 to 12 April 1917, was part of the opening phase of the British-led Battle of Arras, a diversionary attack for the French Nivelle Offensive.
The Victoria Cross (VC) is the highest award of the United Kingdom honours system.
 It was previously awarded to Canada and other Commonwealth countries, most of which including Canada have established their own honours systems and no longer recommend British honours.
 Today, the Victoria Cross (French: "Croix de Victoria" ), created in 1993 and named in honour of the British Victoria Cross is the highest award within the Canadian honours system, taking precedence over all other orders, decorations, and medals.
 It is awarded by either the Canadian monarch or his or her viceregal representative, the Governor General of Canada, to any member of the Canadian Forces or allies serving under or with Canadian military command for extraordinary valour and devotion to duty while facing hostile forces.
 Whereas in many other Commonwealth countries the relevant version of the Victoria Cross can only be awarded for actions against the enemy in a wartime setting, the Canadian government has a broader definition of the term "enemy", and so the Victoria Cross can be awarded for action against armed mutineers, pirates, or other such hostile forces without war being officially declared.
 Recipients are entitled to use the post-nominal letters "VC" (for both English and French) and also to receive an annuity of C$3,000.
 The decoration has not been awarded since its inception.
William Johnstone Milne VC (21 December 1892 – 9 April 1917) was a Canadian soldier.
 Milne was a recipient of the Victoria Cross, the highest and most prestigious award for gallantry in the face of the enemy that can be awarded to British and Commonwealth forces.
 Milne was a Canadian soldier in World War I who received the VC at the Battle of Vimy Ridge on 9 April 1917.
List of Irish Victoria Cross recipients lists all recipients of the Victoria Cross (post-nominal letters "VC") born on the island of Ireland, together with the date and place of their VC action.
 The Victoria Cross is the highest war honour of the British Empire and the Commonwealth of Nations.
 The whole island of Ireland was part of the United Kingdom until 1922 when it was partitioned into Northern Ireland and the Irish Free State.
 In 1948 the Irish Free State became the Republic of Ireland and left the Commonwealth in 1949.
 Despite this, citizens of the Republic still enlist in the British Army and thus are eligible for the Victoria Cross.
William Johnstone, 2nd Earl of Annandale and Hartfell, 1st Marquess of Annandale KT (17 February 1664 – 14 January 1721) was a Scottish nobleman.
 He was the son of James Johnstone, 1st Earl of Annandale and Hartfell and Henrietta Douglas.
 He succeeded to the Earldom of Annandale and Hartfell on the death of his father in 1672.
John William Johnstone Jr. (born November 20, 1946) is an American former professional baseball player, active from 1966 to 1985 for the California Angels, Chicago White Sox, Oakland Athletics, Philadelphia Phillies, New York Yankees, San Diego Padres, Los Angeles Dodgers, and Chicago Cubs.
 Johnstone was known as a versatile outfielder with a good sense of humor, known for keeping clubhouses loose with pranks and gimmicks.
 He later served as a radio color commentator for the Yankees (1989–1990) and Phillies (1992–1993).
William Johnstone VC (6 August 1823 – 20 August 1857) was a Royal Navy sailor and a recipient of the Victoria Cross, the highest award for gallantry in the face of the enemy that can be awarded to British and Commonwealth forces.
 He enlisted and served as John Johnstone.
Steven Milne (born 5 May 1980) is a former Scottish footballer who played as a striker for Dundee, Forfar Athletic, Plymouth Argyle, St. Johnstone, Ross County and Arbroath.
 Milne received a runners-up medal in the 2003 Scottish Cup Final, where Dundee lost 1–0 to Rangers.
 He won the Scottish Challenge Cup in 2007 and the Scottish First Division in 2009 with St. Johnstone.
Nellie Johnstone No. 1 was the first commercially productive oil well in Oklahoma (at that time in Indian Territory).
 Completed on April 15, 1897, the well was drilled in the Bartlesville Sand near Bartlesville, opening an era of oil exploration and development in Oklahoma.
 The well was backed by George B. Keeler and William Johnstone, traders who had a store near the Osage Indian Agency on the Caney River, and was named for Johnstone's daughter.
 Keeler and Johnstone, together with partner Frank Overlees and their Native American wives, took out a lease from the Cherokee Nation on an area of oil seep and enagaged the Cudahy Oil Company to drill.
 The well went to 1320 ft , and was completed using a then-usual technique of dropping a nitroglycerine charge into the well to fracture the bore and release the oil.
 Keeler's stepdaughter Jennie Cass dropped the "go devil" charge in front of fifty spectators.
 The ensuing gusher produced between 50 and 75 barrels a day, and had to be capped for two years until means could be found to move the oil to a market.
The Victoria Cross (VC) is a military decoration awarded for valour "in the presence of the enemy" to members of the Australia Armed Forces.
 It may be awarded to a person of any in any service, and to civilians under military command.
 Being the highest award in the Australian Honours Order of Wearing, the Victoria Cross takes precedence over all other postnominals and Australian orders and decorations.
 The Victoria Cross was instituted by Queen Victoria in 1856, initially to reward acts of valour during the Crimean War.
 Because of its rarity and inherent significance, the VC is highly prized, both as an award and as a collector's item, with one medal being sold for over A$1 million at auction.
 Australians have received the Victoria Cross under the Imperial honours system and later under the Australian Honours System, when in 1991 a new but equivalent award was established by letters patent within the Commonwealth of Australia and its Territories, known as the Victoria Cross for Australia.
 The Victoria Cross for Australia has been awarded four times: twice to Special Air Service Regiment members, once to a member of the 6th Battalion, Royal Australian Regiment, and a posthumous award to a member of the 2nd Commando Regiment.
 All four were for actions in the War in Afghanistan.