I think there's some confusion between two different operations here. Operation Jubilee (or the Dieppe Raid) of August 1942, and Operation Biting (or the Bruneval Raid) of February 1942. Both were planned by the Combined Operation Headquarters.

It was the Bruneval Raid where the primary objective was to steal conpenents of the short-range Würzburg radar system. It was a much smaller operation than the Dieppe Raid, and it was a huge success.

Of 120 Allied troops, two were killed, six were wounded, and six were captured. The men took back key components from the radar system, plus a captured German radar technician, that gave the Allies vital insights into the enemy's advances in radar technology and how to neutralise them.

The Dieppe Raid, which happened a few months later, was the result of some pretty multi-faceted and complex factors. Diplomatic, political, military and covert elements all went into the rationale for it.

First, the diplomatic. There was mounting pressure from the Soviets to open a second front in Europe. The British and Americans could not agree on any element of this grand strategy except for a series of medium-sized raids along the French coast, which is what ended up being implemented.

Also, the British surrender in Tobruk, Libya in June 1942 had seriously damaged British prestige in the eyes of the Americans, at a time when Churchill was trying to lobby the Allied coalition on grand strategy.

Linked to this were the political considerations. The press and the public in Britain were desperate for a second front in Europe, which put pressure on Winston Churchill and his government to do something.

Churchill was also under pressure in Parliament, with his wider war strategy being heavily criticised by some MPs. He even faced a vote of no confidence in summer 1942, which could have brought down his government.

He needed to shore up support among Britain's allies, in Parliament and in the country itself, and a direct attack on Nazi-occupied territory seemed like a good option.

Next, the military elements. As you say, the Allies hoped to test their capabilities ahead of a much larger cross-channel assault. The amphibious element was key here: British troops hadn't attempted an opposed amphibious landing since Gallipoli in 1915, and American troops hadn't done so since the American Civil War. The modern doctrines needed to be tested under fire.

Additionally, the Allies wanted to explore how best to seize a port and how to most effectively deploy a large assault fleet. They also needed to try out new types of assault craft and equipment, and test the strength of the German coastal defences.

Finally, the covert elements, of which there were two. One was also a radar-related mission, which may be where the confusion with Operation Biting comes from.

The Germans had built a long-range Freya radar station on a cliff west of Dieppe. A top secret special operation was planned as part of the Dieppe Raid, which entailed a British radar expert called Jack Nissenthall breaking into the station and gathering intelligence on how it worked.

But the station was too heavily defended: Nissenthall and the soldiers accompanying him couldn't get in. Instead, he clambered up behind the station and cut the wires leading to it.

This forced the German radar operators to use radio transmissions to communicate. The Allies intercepted these transmissions and learned a huge amount about German radar placements across the Channel.

There was another secret component to the raid which involved stealing an Enigma machine, which was referred to in documents by the code "a new German respirator".

The British code breakers at Bletchley Park had cracked the Enigma in 1941, revealing the movements of German U-boats, but by spring 1942 the Germans had upgraded from a three-rotor machine to a four-rotor one.

That machine would have been worth a lot, because British food supplies and equipment were once again being disrupted by the U-boat threat.

Unlike Nissenthall's mission though, this one was a total failure and only one of the five men assigned to it made it back to Britain. One was killed, one was badly wounded, and the other two were captured.

So yes, the Dieppe Raid was something of a dry run for a larger amphibious landing that was to come later, but there were also diplomatic, political and covert elements that went into the rationale for it.

The fact that there were a couple of covert elements to the operation does not mean that the raid was a sham or a distraction technique. The stakes were very high for Britain, Churchill, and the Allied war effort more generally.