Drawing on much rare and never before seen footage from diverse film archives, royal navy historian roland r smith creates a powerful film portrait of the royal navy in the early years of the war, reviewing the fleet and recounting some of its earliest action. Pre war material is also featured, with highlights including queen elizabeth at the 1924 spithead review, the home fleet engaged in wargames, the 1937 coronation review at spithead with aerial views and the hood sailing with the ark royal and repulse. All three would shortly be lost. There are comprehensive film reviews of the battleship fleet, aircraft carriers, cruisers and destroyers as well as sloops, corvettes, frigates, minesweepers, armed trawlers, gunboats, fleet tugs, mtbs and submarines. Early engagements featured include the battle of the river plate in which the cruisers ajax, achilles and exeter took on the battleship graf spee, the rescuing of merchant seamen by the cossack and the barham, resolution and ark royal taking part in 'operation menace' off the african coast. The barham is later seen capsizing and exploding after being torpedoed in the mediterranean. As well as fleet reviews and dramatic accounts of early battles, britannia goes to war also looks at how the royal navy changed in response to war, with coverage of the training of new recruits, new tactics to protect convoys in the channel and a new priority on mine sweeping in home waters.