 When Northesk was given the first rate flagship HMS "Britannia" in 1804 he asked for Bullen as his flag captain especially.Initially serving with the Channel Fleet off Brest under William Cornwallis; "Britannia" was sent to join a squadron under Vice Admiral Robert Calder which, in August 1805, was sent to join Nelson off Cadiz.On 30 August, the "Britannia" joined the blockade of the Franco-Spanish fleet and so was present on 21 October for the battle of Trafalgar.