Photo of the
Getting high performance hydros away with their huge props became ever more difficult and relied on accurate and athletic 'chuck's until international competitors in the late 70s returned from Bulgaria with the 'new' bungee system. The photo above shows that it was hardly new as it dates from 1951. The circle at Fleet was in the middle of a large pond so the anchor for the catapult was a concrete filled oil drum, seen here with the elastic still coiled round the anchor.
Photo from the 'Reynolds archive'