Sources

https://webcache.googleusercontent.com/search?q=cache:5SP6vBH-dE4J:https://www.londonderrysentinel.co.uk/news/the-early-origins-of-the-famous-ash-family-1-2101384+&cd=18

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It is with the Siege of 1688/89 that the Ash name continues to be associated. Captain Thomas Ash's 'Circumstantial Journal of the Siege of Londonderry' is recognised as an unbiased account of events, while the interpretations offered by Walker and Mackenzie, who rushed to the printing presses immediately after the conflict, must be awarded the occasional "pinch of salt" treatment.
In fact, Ash's account was not published until 1792 when his granddaughter decided that it deserved attention and we are indebted to her for her foresight.
Thomas Ash was born in 1660 at Eglinton and was educated in Londonderry. In the 1680s he managed his father, John's estates in Co Antrim and at 25 he was appointed Coroner for County Londonderry. He was on active service throughout the Siege, serving firstly as a Lieutenant with Colonel Parke's Coleraine Regiment and afterwards as a captain with Colonel Lance's Regiment.
Richard Doherty, military historian, believes that he may have been a former soldier, as his account of the Siege includes observations that indicate military experience.
As an aside, Captain Ash was the third son of Sarah, John Ash's second wife. John Ash was married three times and had 24 children altogether. He married his third wife, Elizabeth Holland, in 1665 who was mother of 12 of his children, all born at Ashbrook.
By his will of 1680 John Ash disposed of much of his estate to Elizabeth and her children. He died in 1684.