[3] He afterwards was given command of a hoy which, heavily ballasted with stone, was intended to sink at the entrance of the harbour in Goeree (Goeree-Overflakkee) to block in three Dutch ships-of-the-line.

[1] A sudden squall caused the hoy to sink and O'Brien and his crew were rescued, after some difficulty, by a boat from the hired armed cutter Lion.

As Atalante was short-handed, lacking a lieutenant, master, boatswain, and gunner, O'Brien remained on board for three months, harassing Dutch shipping off the Flemish banks, Dunkirk and Gravelines.

[1] His third attempt was made in conjunction with Maurice Hewson and fellow Hussar junior officer Henry Ashworth from the citadel at Bitche on 14 September 1808.

[3] Ocean was the flagship of Admiral Collingwood who promoted O'Brien to lieutenant on 29 March 1809 and appointed him to the third-rate ship-of-the-line Warrior under Captain John William Spranger.

[1] On 29 June O'Brien commanded the boats of Amphion and Cerberus to provide cover to a landing of sailors and marines at Grao (Grado), Italy, which defeated a French force and captured a large quantity of naval stores bound for Venice.

[3][4] O'Brien cut out seven cargo ships carrying shipbuilding timber to Venice and captured the French xebec La Tisiphone and two gunboats, with no British loss of life.

In November he commanded boats from Bacchante, Eagle and Achille which landed at Fesano (Fažana), Istria, and, despite a garrison of 300 soldiers, captured a large quantity of oak timber owned by the French government.

[3][4] O'Brien was promoted to commander on 22 January 1813 and left Bacchante in April, returning to England as a passenger on Watkin Owen Pell's Thunder.

[3] O'Brien was promoted to captain on 5 March 1821 and left South America in October, returning to Britain on board the frigate Owen Glendower.

He died at Yew House, Hoddesdon, Hertfordshire, on 13 May 1857 and was commemorated in a memorial window in St Augustine's Church, Broxbourne.