There was an article in flypast ages ago about Hamilcar? gliders and they were sending them off training so they were towed up by a tug, released and landed back on the airfield, they were very busy and one they hooked up spiralled down and landed on, when no crew were seen to get out some bods were dispatched to see if they were ok...... it was empty, in the rush to get them off they had hooked up an empty glider that did the sortie on its own.