Rooted in the historical coincidence of the Battle of the Boyne and the Battle of the Somme sharing the date of July 1, more than two centuries apart, Frank McGuinness’s titling of Observe the Sons of Ulster Marching Towards the Somme suggests the clinical detachment of an anthropological treatise — which in some senses it is in its analysis of the noblest and meanest aspects of patriotism and sectarianism.

In a memory play recollected by the sole survivor in a guilt-ridden dialogue with the dead, we witness the initiation, bonding and pairing of eight volunteers in the Royal Ulster Brigade of the British army.

The new recruits come from all parts of Ulster, all walks of life: an unpredictable, sardonic sculptor, a lapsed preacher, a miller, a dyer, a pair of tough workers from the shipyards of Belfast, young men from Derry, Enniskillen or Coleraine, united in their fierce Ulster patriotism and their staunch anti-fenianism. No surrender.

On a large and elegantly symmetrical set — although supplied with an ecclesiastical addendum that could perhaps be left to the imagination — we observe the volunteers in training camp, establishing a pecking order and developing camaraderie; we observe the four pairs of buddies on leave after their first tour of duty; and we observe them, finally, on the eve of the Battle of the Somme, when they parodically re-enact the long-ago battle between the forces of King James and King William, before going over the top, with the smell of two rivers in their nostrils, and all too aware of their own mortality and historical redundancy.

“We’re not making a sacrifice. We are the sacrifice.”

A moving play of lost comrades and lost causes is marked by strong ensemble performance, led by Fred Hawksley as the lone and lonely survivor and Jason Card as his rebellious younger self, capably supported by Chris Woodford, John Cheeseman, Matthew Verge, J. Pius Bennett, Anthony Fushell, Ken Martin and Ray Saunders as his doomed comrades in arms.

Angry and loving, haunted and passionate, it is a thoughtful piece, if sometimes over-declarative and message-heavy.

While the first movement is easy and natural, the second is more theatrically contrived, the dialogue more strained, as the trauma of battle experience is evoked.

The final movement does not entirely avoid over-messaging, but it nonetheless intriguingly fuses the meaning of the Boyne and the Somme — and perhaps of all patriotic wars, if it comes to that.

Designed and directed by Clar Doyle, the Beothuck Street Players production of Frank McGuinness’s Observe the Sons of Ulster Marching Towards the Somme continues at the LSPU Hall until Saturday.

Showtime is 8 p.m. With one intermission, curtain call is taken at 10:30 p.m.