SIR,--I have the honour to inform you, that immediately after my arrival at _Monte Video_, on the 10th of May, I began to make every possible preparation for the attack of this place, as the first and most essential step towards the reduction of the province. For this purpose sloops of war and other light vessels were sent to reconnoitre the southern bank of the river, in order to fix upon the precise point of debarkation. It was found that the water was too shallow to admit of a landing, under cover of the ships of war, anywhere to the westward of the town of _Buenos Ayres_, nor nearer to it on the eastward than the _Enseñada_ of _Barragon_. This bay was, therefore, fixed upon as the point of debarkation, and every arrangement that could previously be made was pressed forward with expedition, whilst I waited anxiously for the arrival of Brigadier-General Craufurd’s corps, and the fleet with which I had sailed from England. On the 27th of May, Rear-Admiral Murray and Brigadier-General Craufurd arrived at the mouth of the river; but owing to a prevalence of contrary winds, the expedition did not reach Monte Video until the 14th of June. I immediately determined not to wait the arrival of the convoy from England, as by the general voice of the inhabitants, and of those officers who had passed the winter in the province, the months of July and August were represented as most unfavourable to military operations, on account of the heavy and continual rains which prevail at that season. Having fixed upon _Colonia_ as the place of assembly from which the expedition was to proceed, I sent the troops upwards, in small divisions, on account of the intricate navigation, leaving at _Monte Video_ the 47th regiment, the detachments of the 20th and 21st light dragoons, two companies of the 38th regiment, and a corps of militia, formed by the British merchants, in all composing a garrison of about 1300 men, under the command of Colonel Browne, of the 40th regiment; and after much delay, caused by contrary winds, Rear-Admiral Murray and myself arrived opposite the point of debarkation on the 28th ultimo.