Lieutenant Colonel Martyn was born on the 4th of February 1888 in Mansfield, Nottinghamshire to Ernest and Agnes Martyn. He commissioned into The Sherwood Foresters as  2nd Lieutenant with the 1/8th Battalion on the 22nd of October 1908. He steadily rose in rank becoming a Lieutenant (on the 26th of January 1910), Captain (on the 4th of August 1914), Officer Commanding with “D” Company (on the 22nd of April 1915) and Major on the 13th of October 1915. 

He was in the Irish Rebellion of 1916 with 2/8th Battalion and was awarded the Military Cross (MC) which was reported in the London Gazette on the 24th of January 1917: 

‘On 27th April 1916, reports were received that Leeson Bridge and Square (Dublin) were held in force by Sinn Feiners. The South Dublin Union was flying the Sinn Fein flag and was strongly occupied. Lieutenant Colonel Oates ordered Captains Martyn and Oates to attack the building and thus clear the right flank as the fire from the union commanded the bridge. Some fierce fighting occurred, but with great gallantry, Captains Martyn and Oates succeeded in making a breach in the wall and with great dash reached the enemy barricade. A grenade was thrown at the enemy but it hit the barricade and rolled back landing at the feet of the attacking group. Captain Martyn picked up the grenade and threw it over the barricade at the enemy. They then held a portion of the Union which caused the enemy fire to slacken and enable the rest of the Brigade to pass over the bridge and carry on the advance to the Royal Hospital at Kilmainham.’ 

He returned to France with 2/8th as Lieutenant Colonel. He then commanded the 2/7th (Robin Hood) Battalion and was awarded the Distinguished Service Order (DSO). It was reported in the London Gazette on the 17th of December 1917: ‘for conspicuous gallantry and devotion to duty at Ypres on 26.9.1917 in rallying and reorganising his men at the furthest objectives when men of other units besides his own were wavering under a heavy barrage and enemy preparations for counter attacks and so adverting a serious situation.’ 

He was Temporary Command Brigade as Lieutenant Colonel with 6th Battalion Royal Leicestershire Regiment and was reported missing on the 25th of August 1918 after being taken prisoner by the Germans. He was repatriated on the 13th of February 1918.