Aylmer is primarily known as the commander of the force that penetrated the Gironde in July 1815, as part of a wider British strategy to rally French royalists against Napoleon.

[1] Aylmer joined the navy shortly after his thirteenth birthday, as a captain's servant to John Manley, on board the 32-gun frigate, HMS Syren, in the Channel.

[1] Promoted to lieutenant in December 1796, Aylmer transferred to HMS Swiftsure the following January, and sailed to the Mediterranean under Captain Benjamin Hallowell Carew, where he participated in the Battle of the Nile.

[2] In January 1802, following a protracted period of shore leave, Aylmer returned to the Mediterranean, joining Lord Keith's squadron as commander of the 18-gun sloop Delight.

The allies held the town for three days against a force of 700 to 800 French troops before retiring on 8 July, after putting around 150 of the enemy out of action, and destroying the guns of the forts at Santoña and Laredo.

[5] On 9 August, after the town was shown to be manufacturing arms and assisting in the destruction of British ships off the coast of New London, the brig, Dispatch anchored close to a shore battery and opened fire.

[5] In July 1815, Aylmer commanded a small force which sailed up the Gironde and entered Bordeaux, which although garrisoned by Imperial troops was largely sympathetic to the Royalist cause.

[1][6] Aylmer's ship, Pactolus, arrived at the mouth of the estuary on 3 July and immediately an Aide-de-Camp was despatched under a flag of truce, to open a dialogue with General Bertrand Clausel, who was commanding the armies in the area.

[9] On 13 July, the small squadron comprising Pactolus and Hebrus, each with a transport in tow, together with Falmouth, entered the mouth of the estuary and soon after doing so were met by a delegate from Royan who gave an undertaking that the town’s guns would not fire upon them, providing the courtesy was reciprocated.

[1][9] Although the fort at Verdon did open fire, the British did not retaliate and after anchoring, a delegation, headed by the Comte de Lasteur, was sent to once again try and establish contact with Clausel while Falmouth was sent home with dispatches for Lord Keith.

[9] Aylmer thought it prudent to destroy all enemy forts and guns within range of the river in order to secure a line of retreat, and so set about putting the batteries of Royan out of action.

On the 16th, the British sailed further up the river towards Castillon having destroyed the forts of Verdon, Royan de Lousac and Miche, and 70 other pieces of artillery along the mouth of the estuary.

[11][12] A British fleet under Edward Pellew, comprising six line-of-battle ships, four frigates, nine smaller warships, a naval transport, a sloop and a despatch-vessel, left Plymouth at 12.00 on 28 July.

[15] Having been promised a reply within two hours, and having still not received one by 14:00, the British delegate, Lieutenant Burgess, returned to Severn and Pellew then gave the order for the fleet to take up position.

He was also awarded the royal order of St Ferdinand and of Merit for transporting freed Italian slaves to Naples together with the sum of money repaid by the Algerians.