The Dieppe Guinea Pigs

August 19, 1942:

The Dieppe Raid, also known as the Battle of Dieppe, Operation Rutter and, later, Operation Jubilee, was a Second World War Allied attack on the German-occupied port of Dieppe. The raid took place on the northern coast of France on 19 August 1942. The assault began at 5:00 a.m. and by 10:50 a.m. the Allied commanders were forced to call a retreat. Over 6,000 infantrymen, predominantly Canadian, were supported by limited Royal Navy and large Royal Air Force contingents.
The objective of the raid was discussed by Churchill in his war memoirs: "I thought it most important that a large-scale operation should take place this summer, and military opinion seemed unanimous that until an operation on that scale was undertaken, no responsible general would take the responsibility of planning the main invasion". Churchill continues: "In discussion with Admiral Mountbatten it became clear that time did not permit a new large-scale operations to be mounted during the summer (after Rutter had been cancelled), but that Dieppe could be remounted (the new code-name "Jubilee") within a month, provided extraordinary steps were taken to ensure secrecy. For this reason no records were kept but, after the Canadian authorities and the Chiefs of Staff had given their approval, I personally went through the plans with the C.I.G.S., Admiral Mountbatten, and the Naval Force Commander, Captain J. Hughes-Hallett." Objectives included seizing and holding a major port for a short period, both to prove it was possible and to gather intelligence from prisoners and captured materials, while assessing the German responses. The Allies also wanted to destroy coastal defences, port structures and all strategic buildings. The raid could have given a morale boost to the troops, Resistance, and general public, while assuring the Soviet Union of the commitment of the United Kingdom and the United States. Research published in 2010 proposes that the Dieppe raid was also a "pinch" raid for the Naval Intelligence Division (NID) overseen by Ian Fleming. A group of No. 30 Commandos were sent into Dieppe to steal code books, setting sheets and a German-made Enigma code machine for encryption and decryption of secret messages.
No major objectives of the raid were accomplished. A total of 3,623 of the 6,086 men (almost 60%) who made it ashore were either killed, wounded, or captured. The Royal Air Force failed to lure the Luftwaffe into open battle, and lost 96 aircraft (at least 32 to flak or accidents), compared to 48 lost by the Luftwaffe. The Royal Navy lost 33 landing craft and one destroyer. The events at Dieppe later influenced preparations for the North African (Operation Torch) and Normandy landings (Operation Overlord).

Well, it wasn't as large of a failure as Churchill's Gallipoli campaign, but the Dieppe Raid resulted in a stunning 68% casualty rate.  That is amazingly bad.