Britannia was launched in 1762 as the sistership of the Royal George of 1756. Britannia was laid down in 1752, launched in 1762 but not commissioned until 1778 for the american war of independence in the european theater.
at 178 ft on the gundeck and 52 ft on the beam weighing 2,091 Tons BM she took the title of largest british three decker from her sister when she was launched. Her armament consisted of 28x42 lbs guns, 30x24 lbs guns, 30x12 lbs guns and 16x6lbs guns. Interestingly she would become one of the last british 1st rate ships to retain 42 lbs guns on her lower gundeck, keeping them until 1807.

HMS Britannia would go on to have a very decorated career and rivals HMS Victory's Battle honors.
She would also become the only other british first rate to serve with HMS Victory through 7 different battles.
2nd Battle of Ushant 1781 with Victory
Relief of Gibraltar 1782 with Victory
Battle of Cape Spartel 1782 with victory
Siege of Toulon 1793 with Victory
Action off Genoa 1795
Battle of Hyeres Islands 1795 with Victory once again
Battle of Cape St Vincent 1797 with Victory
Battle of Trafalgar 1805 with Victory and Royal Sovereign.

Renamed Saint George in 1812 and Converted into a prison ship in 1813
Started fitting as base flagship and receiving ship at Portsmouth in 1815
then Flag ship at Plymouth as a 100 gun first rate
Renamed Barfleur in 1819 before being broken up in 1825 after 63 years of service in the Royal Navy

Thanks for Viewing as always notice that this ship is sister to the Royal George so they are very similar and i copy pasted my royal george and changed it to fit britannias model,