Lamellerie's expedition was a French naval operation launched in February 1806. Four French Navy frigates and a brig, all survivors of the Battle of Trafalgar in October 1805, attempted to break past the British blockade of Cadiz on 23 February 1806, taking advantage of the withdrawal of the principal blockade squadron several months earlier at the start of the Atlantic campaign of 1806. Although the squadron was intercepted by elements of the British blockade force, Captain Louis-Charles-Auguste Delamarre de Lamellerie escaped with the four frigates by abandoning the slower brig, which was captured. During the next six months, Lamellerie's squadron cruised the Atlantic, visiting Senegal, Cayenne and the West Indies but failing to cause any significant disruption to British trade.
On 27 July, as the squadron neared Rochefort, it was spotted by HMS Mars, a Royal Navy ship of the line stationed off the port to intercept French ships entering or leaving. Signalling to the rest of the British squadron, Captain Robert Dudley Oliver took Mars in pursuit, chasing the French squadron all through the night and into the next morning, by which time the frigate Rhin had fallen far behind the others. Recognising that Rhin was in danger of being captured, Lamellerie turned back to her defence with his main squadron but then changed his mind, turning once more and retreating to Rochefort as Oliver took possession of the heavily outgunned Rhin.