alternatehistory.com

10 June

As dawn breaks, Pennefather launches his assault on the Union positions north of the Grand river.
Four 40-lber Armstrongs arrived on the 8th, and he has spent the 9th registering them in on their targets - firing one round every half hour or so, to obscure his motives. Now these, and all his 12-lber Armstrongs (in specially built earth-ramp cradles which cause them to return to battery under their own gravity) deliver a snap bombardment at maximum rate.
Also adding to the general cacophany are the Pisces, Capricorn and gunboat Ripple, all bombarding the western end of the line. The storm of bombardment is incredible, with over a hundred shells bursting over or in the Union defences per minute for five minutes, and it also serves as a signal - three battalions British and Canadian infantry begin their crossing of the river, using assault boats built over the last three weeks supplemented by the small boats they have managed to capture.
To his credit, Blair defends tenaciously. The guns he has managed to preserve are well masked at the level of the river, and open up on the British assault boats - sinking several, mainly by use of the 'skip' technique to hole the boats. This leads to the loss of several hundred British and Canadian soldiers, but roughly two battalions make it over the river and begin to advance.
Pennefather's artillery retargets a little slowly, the cradles making it hard for the gunners to lay their pieces on the new targets, and it is a Canadian battery armed with smoothbore 9-lbers (the Loyal Company of Artillery) which disables three of Blair's guns - earning them much praise and a much-deserved spot in the history books. (Their time-fuzes are set with great precision, and the hail of shrapnel renders the weapons impossible to effectively use until Armstrong fire can concentrate on and destroy the gun carriages.)
Somewhat disorganized by the river crossing, the British/Canadian brigade reverts to training and spreads out in skirmish order. They advance slowly, gaining a portion of the defences against Union infantry still reeling from the opening bombardment, and hold on against two fierce counter-attacks (both of them repelled bloodily by well-aimed rifle fire, though on one occasion the commander of one Canadian militia battery requests permission to perform a bayonet charge!)
Pennefather has the two Zodiac ironclads brought in close to the southern shore to load reinforcements onto them (an evolution aided by their very low draft) and the 2/6th are ferried across to reinforce the penetration.
As they disembark, however, Blair raises the white flag.

It turns out that the Governor of Michigan's forces were simply stretched too thin. Needing to cover several miles of the Grand River, as well as defend his rear in case of a British landing on the long coasts of Lower Michigan, has resulted in a position given the appearance of strength more than the reality - with the second counterattack repelled, the closest fresh Union troops are four miles away (an hour's march) and he knows he will not be able to prevent Pennefather shipping his entire army over.

As a point of curiosity, the 17th Wisconsin do not surrender with the rest of the army. Their commander, Col. John L. Dornan, marches them up Michigan and across to Upper Michigan, and thence to Wisconsin - an impressive feat of logistics. (It is not reported if he had read the Anabasis).

Pennefather makes the preparations for some of his Canadian militia to garrison Lower Michigan - relying on the Royal Navy to protect the coasts - and marches for Detroit the next day. Union prisoners march along with the column, to go into captivity at or around Windsor.