As part of the preparatory effort against the German defences in northern France, the panzer training camp northeast of Paris at Mailly-le-Camp was targeted for destruction. The camp was French, built for their armoured formations, but since the fall of France the Germans had been using it to train replacement crews for units refitting from losses suffered in the east. Cheshire with his four marker Mosquitos from 617 were tasked with marking the target, and 346 Lancasters from 1 Group and 5 Group were tasked with destroying it. On the night of 3/4 May Cheshire approached the target for a typical low marking technique raid, with Cheshire and Shannon making the initial marking, and Lancasters from 83 Squadron and 97 Squadron serving as back-up marker aircraft. An assembly point marker was dropped 15 miles away from the target, and the aircraft of the two groups of heavy bombers were ordered to orbit it at stacked altitudes of 100 feet separation while awaiting instructions to attack. Unbeknownst to Cheshire, that night the US Armed Services Radio was broadcasting big band swing music on the same frequency Cheshire was using for his raid. Arriving over the target, an illumination flare provided excellent visibility and Cheshire swept in and marked it, but when the Main Force Controller went to call in the waiting Lancasters no one received his message. Meanwhile, Luftwaffe night fighters began to arrive. It was a clear night with a full moon, and soon the night fighters got in amongst the circling bombers. The air combat over France that night was short, but intense. Crews reported seeing four or five Lancasters falling from the sky at a time. 5 Group lost 14 bombers, while 1 Group making up the second wave lost 28. After a delay of some 15 minutes the Deputy 'Main Force Controller' took over and ordered the bombers in. The training base at Mailly-le-Camp was hit heavily. 114 barrack buildings, 47 transport sheds, 65 vehicles and 37 tanks were all destroyed in the attack, while 218 soldiers were killed and 156 more were wounded. However Bomber Command suffered the loss of 42 Lancasters and their crews, with another Lancaster written off after it made it back to base. The training base was destroyed, but Bomber Command suffered a loss rate of 11.6%.