"Attack on Cloudbase" begins with Spectrum fighter pilot Symphony Angel being forced to eject into the Sahara when her aircraft is damaged. Later, a fleet of Mysteron spacecraft enter Earth's atmosphere and launch a devastating assault on Spectrum's airborne headquarters, Cloudbase. Filmed in late 1967, the episode underwent a number of script changes prior to shooting. Gerry Anderson chose Ken Turner to direct due to its unusual nature of the story. The episode presented Century 21's special effects team with several technical challenges, including a scene in which a miniature Angel aircraft overflies the puppet of Symphony Angel in the same shot. For the attack sequence, only a small number of spacecraft models were made; flashing light bulbs were placed in the backdrop as a cost-effective way to create the illusion of a larger fleet. Series composer Barry Gray wrote a full score after Anderson decided that none of the incidental music in Century 21's library suited the episode's grim tone.