[5] Thomas Ussher entered the Royal Navy on 27 January 1791[6] at the age of 12[3] as a midshipman on board the 24-gun sixth-rate Squirrel, under the command of Captain William O'Bryen Drury.

Invincible was present in the battle of the Glorious First of June, 1794, during which Ussher took part in the capture of the French 80-gun ship Juste, subsequently serving aboard her for a year in the English Channel.

[6] During operations in May 1796 against Saint Lucia, Ussher, who had been appointed acting-lieutenant of the Minotaur (74), under Captain Thomas Louis, was employed on shore in command of a party of seamen attached to the army under Sir Ralph Abercromby.

[6] Ussher rejoined the Pelican on 27 September 1797, and took part, while the ship was under the temporary command of Lieutenant Thomas White, in the destruction of Le Trompeur, a French privateer of 16 guns and 160 men, not far from Santo Domingo.

[6] On 2 April 1798 Ussher was sent out in command of two boats containing 14 men to search various creeks in Cumberland Harbour and St. Jago de Cuba for a privateer which had been raiding the coast of Jamaica.

[6] The next day, 5 April, while reconnoitring the mouth of the river Augustine, near Cumberland Harbour, he observed the French privateer schooner, Le Moulin a Cafe, of 7 guns and 83 men, which was lying across the stream, with her bows apparently aground and most of her crew on shore.

[7] In July 1799 he commanded the boats in the capture of a Spanish vessel at Laguira having entered the port in an attempt to retake the British frigate Hermione, which unfortunately had sailed a few days previously.

[8] In September 1800 Trent returned to England with Admiral Sir Hyde Parker aboard, and Ussher, still suffering from the effects of his wounds, was obliged to go on to half-pay.

Ussher applied for employment in June 1801, against the advice of his doctors, and was appointed to command the cutter Nox, stationed off Weymouth in attendance upon the King, where he remained four months.

On 6 April 1804 he was appointed to command of the hired armed brig Colpoys, of fourteen 12-pounder carronades and a crew of 40, which was attached to Admiral William Cornwallis's blockading force off Brest.

[8] Towards the end of 1804 Ussher was assigned to be the second-in-command to Captain Peter Puget in a proposed operation to destroy the fleet at Brest by means of fire ships.

However a succession of winter gales blew the British fleet from the coast; and on regaining his station Cornwallis was in some doubt as to whether or not the enemy had left port.

Ussher, of his own accord, that night sailed inshore and took his gig (a 4-oared boat) into the harbour and rowed along the whole French line, gaining an precise knowledge of the enemy's force, which consisted of 21 ships.

On 19 April 1806, 24 men from Colpoys and the gun-brig Attack, under Lieutenant Thomas Swain, landed at the entrance of the river Doelan, spiked two guns of a battery, and captured two chasse-marées.

[8] Soon afterwards, with the gun-brig Haughty and cutter Frisk under his orders, he volunteered to cut out a French frigate lying at San Sebastián, but was prevented by contrary winds from reaching the port before the ship had sailed.

His conduct at Avilés had previously obtained for him a sword valued at £50 from the Patriotic Society; and he had the satisfaction of receiving from the crew of the Colpoys a similar token of their "respect and esteem.

In March 1807 while escorting a convoy through the Straits by Tarifa, he succeeding in decoying an enemy flotilla within range of his guns before forcing them to seek safety under their land batteries.

On 7 September, returning from conveying despatches to the Balearic Islands, Redwing drove several vessels ashore near the town of Calassel, on the coast of Catalonia, and would have taken or destroyed them, had not a violent thunderstorm prevented it.

However the abdication of King Gustav IV Adolf of Sweden, altered the plans of Government, and she was not employed in any particular way until the commencement of the Walcheren Campaign in July 1809.

[9] Leyden was paid off in January 1810, and on 15 May 1811 Ussher was given temporary command of the America (74), transferring to the ship-sloop Hyacinth (26) on 24 May to accompany a fleet of merchantmen to the Mediterranean, where he joined the squadron engaged in the defence of Cádiz.

[9] On the night of 29 April 1812, having assembled the boats of Hyacinth, the sloop Goshawk, the gun-brig Resolute, and Gun-boat No.16, he attacked several privateers, commanded by "Barbastro", lying in the port of Málaga.

[9] On 26 May 1812, in co-operation with Spanish guerrilleros, Ussher, with Hyacinth, the sloop Termagant, and the gun-brig Basilisk, attacked the castle of Almuñécar, which was armed with two brass 24-pounders, six iron 18-pounders, and a howitzer, and defended by 300 French troops.

[12] On 18 August 1813 an attack was made upon Cassis, between Marseille and Toulon, by Undaunted, the brig Redwing, and the 16-gun brig-sloop Kite, reinforced by boats from the ships Caledonia, Hibernia, Barfleur and Prince of Wales.

[13] In late 1813 Ussher was stationed by Sir Edward Pellew off Toulon with a small squadron under his orders to watch the movements of the French fleet.

[11] In April 1814 while off Marseille, and in company with Euryalus, Captain Charles Napier, Ussher received a deputation, consisting of the mayor and civil authorities of the city, who informed him of the abdication of Bonaparte, and of the formation of a provisional government.