William was the captain of the HMS CALLIOPE. He was mortally wounded in the battle of the New Zealand land wars fought between Ngâti Toa Mâori, and a colonial force of European troops, police, and Ngâti Awa allies.

There is an excellent site with the story from which I have taken this short description: Porirua, 10th August, 1846.
"Sir – At daylight on the morning of the 5th instant I proceeded in the boats for her Majesty's ships Calliope and Driver up the harbour of Porirua, landed about a mile and a half distant, and pressed forward into the Horokiri Valley five or six miles, over a road almost impassable to troops. … We passed encampments the enemy had recently left, leaving behind them the bugle taken from the troops in the attack on Boulcott's Farm.
At half-past two p.m., we came up with our Native allies and a party of militia under the command of Captain M'Donough, who were lying at the foot of a precipitous hill covered with wood, near the summit of which the enemy were supposed to be posted.
The troops then commenced hutting themselves for the night. On the following morning I gave orders for the advance, directing the Native allies to proceed on to cover it.
The first division, consisting of seven officers and 127 men of the force, made up of seamen, soldiers, militia and armed police, was under the command of Major Arney, 58th Regiment.
The second division, of five officers and 117 men of similar detail was under the command of Captain Armstrong, 99th Regiment. At about 9 a.m. we ascended the hill, preceded by an officer and a party of men with tools to cut away the wood. … After ascending with great difficulty about a mile, we suddenly discovered that the enemy had established himself in a stockade on the spur of a hill, which was not only excessively steep and precipitous upon each side, but so narrow in places that only a few men could proceed abreast.
"The stockade that was visible appeared very strong, composed of heavy logs of timber placed horizontally one over another, with loopholes to fire through.
Some of the enemy having appeared in front, a heavy fire was opened on both sides; they made repeated attempts to turn our left flank, but were driven back with great loss (!) to their position.
… Our loss was severe, having two killed and nine wounded, as will be seen by the annexed return : –
"Killed – Ensign H.M. Blackburn, 99th Regiment; Private Thomas Tuite, 99th Regiment.
"Wounded – W. Roberts, captain of missen-top H.M.S. Calliope, mortally, since dead; Private John Carr, 58th Regiment, slightly; Private Robert Miller, 65th Regiment, severely; Private Patrick Darcey, T. Woodfield, F. O'Reilly, J. Henchcliff and J. Booth, 99th Regiment; Private George Farmer, militia, severely.
"All these casualties occurred in the action of August 6th
"The firing lasted till dark, when, finding my position unfavourable to occupy at night, I left two officers and 120 men to assist our Native allies to watch the enemy, and again took up the post I had left in the morning. The enemy admitted to have lost five killed and two wounded; among the number one chief named Te Oro, and Tapuke, the murderer of Richard Rush at the Hutt."