The fourth Ajax started life as the sixth HMS Vanguard and was built at Pembroke and launched on 25 August 1835 and commissioned in 1837. She was built at a total cost of £78,000.
She was a 78-gun (80 when launched) second rate ship of the line of the Symondite design. Crew: up to 750 officers & men. 2900 tons; length 190 ft; beam 57 ft. Armament as launched: 68x 32 pounders; along with 4x 68 + 4x 32 + 4x 18 pounder carronades (Short barrelled cannons)
On 20 Oct 1867 the Vanguard was renamed Ajax to allow the name Vanguard to be given to a new iron-clad battleship.
Ajax was broken up in 1875 at Chatham.