The third HMS Ajax was launched on the Thames on 2 May 1809.
She was another 74-gun third rate ship of the line, fully rigged sailing ship. 1761 tons, length 176 ft; beam 47 ft. Armament: 28x 32 pounders; 28x 18 pounders; 6x 12 pounders; along with 12x 32 pounder carronades (short barrel cannons); & 6x 18 pounder carronades.
She received Battle Honours at the Battle of San Sebastian, Spain in 1813.
In 1846 she was converted to a costal defence screw propulsion blockship, or steam guardship, which involved removing her ballast, copper, some bulkheads, cutting her down to a single deck and fitting a 450hp steam engine.
Although intended for defence work, blockships were often used offensively and Ajax saw service in 1854-55 in the Crimean War in the Baltic at which she received another Battle Honour.
She was finally broken up in 1864.