The cost of defending the Channel Islands

How would the war change if Churchill chose to defend the Channel Islands?

They could become a valuable radar and denial position, but only if fortified early and sustained as an isolated military fortress under constant attack.

Defending the Channel Islands would require fortifications and a dug-in garrison prepared before the war, followed by a sustained supply effort. Some islands appear more defensible than others, and keeping aircraft operating there would need special arrangements. An Allied position so close to occupied France could obstruct German movement through the Channel and give radar warning of air raids. It could also prompt more Atlantic Wall construction, even if the islands themselves stayed in Allied hands. The price would be civilian evacuation and a garrison living underground under repeated Luftwaffe attack. The suggestion that heavy siege artillery might be used is a panel prediction within this counterfactual.