Major General Isaac Brock was a daring commander and highly effective leader of men. During his short period as leader of British forces in the Canadian theatre he demonstrated rare offensive acumen. The siege of Detroit was one of these engagements which has helped to define his abilities in posterity. In the summer of 1812 General Brock with his small regular force could not take the offensive at any point on the frontier without leaving other points unguarded, and had the Americans been enterprising and efficient his situation would have been impossible.  As it was, his own first move was to the Niagara frontier, where he contemplated an attack on Fort Niagara.  However, he did not attempt this, arguing that it was more important to get on with training the militia; unsurprisingly the Americans made no immediate offensive move in this sector.  Brock then returned to York (now Toronto), the provincial capital, for the session of the legislature.  This gave him an opportunity, in his civil capacity, of addressing himself to the province and giving a strong lead to its people, so many of whom were uncertain and disheartened. 

By the time the Assembly was prorogued, it was clear that for the moment the main threat to Upper Canada was on the Detroit frontier.  Brock immediately launched a vigorous counteroffensive.  Hull's invasion and a bombastic proclamation which he had issued had considerably discouraged the Canadian militia along the Detroit; but when Brock asked those assembled at York for volunteers to march against the invaders, more came forward than transport could be found for.  The general had already ordered a small regular reinforcement to Amherstburg.  He had tried to organize a force to operate on the Thames, but this had been largely frustrated by the unwillingness of the militia in the nearby districts.  He now dispatched 100 militiamen from York to the Long Point district on Lake Erie.  At that place, he wrote to Prevost on 29 July, "I propose collecting a force for the relief of Amherstburg." 

On the night of 5 August, the same day on which he prorogued the Assembly, Brock himself sailed from York for the head of Lake Ontario.  Pushing rapidly on overland to Port Dover, he found the relief force awaiting him there, along with boats to carry them up Lake Erie. (Colonel Thomas Talbot, the redoubtable founder of the Talbot Settlement, had experienced considerable difficulty with the militia of the district, but had finally obtained a fair number of volunteers.) On the 8th Brock embarked his tiny "mass of maneuver", which amounted in all to about 50 regulars and 250 militia with one six pounder, and, coasting along the lake shore, reached Amherstburg and made a junction with the British force there on the night of 13 August.  Poor weather and bad boats had delayed the movement, which nevertheless were rather swift considering the reduced conditions. 

The general immediately divided his whole force into three miniature "brigades", two consisting of militia stiffened by small regular detachments and the third of the main body of the 41st Regiment.  On 15 August orders were issued for crossing the Detroit and moving against the American army.

Few officers would care to cross a broad river with the prospect of attacking on the farther shore a force twice as strong as their own in a fortified position.  Brock himself recorded afterwards that his colonels advised against it.  The general, however, was taking a "calculated risk".  The captured correspondence had told him how low was the Americans' morale and how discouraged their commander and the very fact of their retreat from Canadian territory had further emphasized the poor state of their army.  Even so, his decision remains a fine example of the offensive spirit which wins battles. 

On the evening of 15 August Brock opened fire upon Fort Detroit with five guns which had been emplaced on the Canadian shore.  The bombardment inflicted some casualties and further discouraged the Americans; Brock had made a judicious contribution to the disintegration of poor Hull by sending him a demand for surrender which remarked that, while he did not intend to "join in a war of extermination," the Indians would "be beyond control the moment the contest commences", and soon after daylight on the 16th the little British force crossed the river in boats and landed three miles below Detroit.  The army consisted of some 700 white troops, of whom 400 were militia, and 600 natives, with five small field guns.  The battery opposite Detroit was served on this day by gunners landed from the Provincial Marine.  Although Brock does not mention it, Hull in his apologia emphasizes that the British landed "under cover of their ships of war", and it is clear that co -operation between the land forces and the Marine was close throughout.

Brock had planned to take up a strong position and trust to the effect of his artillery fire to compel Hull to come out and meet him in the open field.  He now received information, however, that a detachment of 500 men had left Detroit three days before and that their cavalry were only three miles to rear of his own force.  Accordingly, he took another bold decision-to make an immediate assault upon Detroit.  The troops advanced upon the fort, but before the attack could begin the American commander sent forward a flag of truce and proposed a discussion of terms.  The sequel was the surrender within an hour of Hull's whole army (including the detachment above referred to), with 35 guns and a great quantity of other arms and stores. 

Thus General Brock had won a resounding victory and entirely removed the menace to the western frontier, almost without firing a shot.  Well might he write to the Commander-in-Chief, "when I detail my good fortune Your Excellency will be astonished." There was, however, more than good fortune to thank for what had happened.  The energy and boldness with which Brock himself had acted were the chief causes of this extraordinary result. 

On Hull's own showing, it was the vulnerability of his communications (constantly exposed to interruption as a result of the British control of the water), and the fear of the natives, that induced him to his ignominious surrender.  As he stated, the loss of Mackinac had “opened the northern hive of Indians" and the expectation of the upper tribes "swarming down" upon his army went far to take the heart out of him.  What the success at Mackinac had done in the case of the natives the capture of Detroit may be said to have done among the white population of Upper Canada.  This brilliant victory silenced the croakers and encouraged loyal citizens. Canadians now realized that a successful defense of the country was quite possible.  The militiamen whom so many had considered dupes suddenly became saviours and heroes, and before the year 1812 was over the Canadian legend that attributes the saving of the country primarily to the militia was already well on the way to establishment.