There are two catagories of effort "Derby" and "Goodwood."

A Derby effort means that operational squadrons had to detail as many crews and aircraft as possible, except crews that had operated on both the two previous nights, and crews in training, Squadron Commanders were not required to fly in a Derby effort. Of the three categories of crews (experienced, fresher, and crews without operational experience), all the experienced crews and as many fresher crews as the Squadron Commander thought fit for operations were required for a Derby effort if the squadron had not operated the prvious night. Once the target was announced, the Squadron Commander could either stick to his initial selection or relieve a few experienced crews and replace them with fresher crews. He was also free to increase the operational experience of his fresher captains and pilots without operation experience by sending them on operations as second dickeys with his main crews.

A Goodwood effort meant that, whatever the target, all main crews would fly, plus all the fresher crews the Squadron Commander considered ready for operations. Once the target was announced, the Squadron Commander could increase his detail by adding more fresher crws, and he could also send any of the unassigned fresher pilots, or any of the pilots without operational experience, as second dickeys with the main crews.

For both Derby and Goodwood efforts, either the Squadron Commander or one of the flight commanders had to stay on the ground and take charge of flying operations.

Source: Thunderbirds at War: Diary of a Bomber Squadron