A great question, garstonite. All of the Halpin's we're interested in were Protestant, but some of them had confusing sympathies for and attachments to Catholics. They themselves say they came from county Louth, in the north east corner of Ireland, and many of them used the surnames Halpin and Halfpenny interchangeably, placing them among the large mix of Catholic and Protestant Halpins and Halfpennys found in Louth. A developing theory of my own is that they were what Irish historians call 'Old English' - that is, they settled in Ireland as colonizers before the English reformation and the conversion of England to Protestantism. Thereafter, over the course of a few generations and in response to events in Ireland and abroad, more and more of them converted, with the last of the conversions occurring between the Cromwellite wars and the Glorious Revolution of 1688. If there were any Catholics left in the Halpin family after that point, they probably converted in response to the Penal Laws, introduced to deprive the native Irish of the remainder of their lands and properties. This seems to me to be the most likely course of events.
Nicholas's line of descendants settled in Portarlington, Queen's County, some time before the 1760s, where they were associated with the education of the Ascendancy's children. I've been trying to link a certain Christopher Halpin, who was a distiller in Dublin in 1798, to the rest of the Halpin clan, and your discovery of a 'Christophe', son of Nicholas, has given me the best indication yet that I might be on the right track. Hence my gratitude and excitement.
So your speculations as to the possible participation of the Halpins in the events surrounding the Glorious Revolution in 1688 and the Anglo Dutch War are certainly not wild. They fit with a trend and a pattern that was repeated in the 18th and 19th centuries. Many of the Halpins were indeed 'fighting men'.