'Constellation' (i) was a British unrealised plan developed by Vice Admiral the Lord Louis Mountbatten’s Combined Operations Headquarters for the recapture of the German-occupied Channel Islands (1943).
Between 1940 and 1945, the Channel Islands were the only fragments of British territory to come under German occupation. The islands were garrisoned by almost 40,000 German soldiers, sailors and airmen, their defences being centred on fortifications whose construction had used more than 10% of the concrete used in Germany’s 'Atlantic Wall' defences stretching from Norway to the Franco/Spanish frontier at the western end of the Pyrenees mountains.
Mountbatten proposed 'Constellation' (i) as a major offensive against the German forces in all of the Channel Islands, as well as smaller operations such as 'Concertina' (i) against Alderney, 'Coverlet' against Guernsey and 'Condor' (ii) against Jersey. Mountbatten suggested that 'There is no doubt that the enemy has fully appreciated the value of the Channel Islands, and the potential threat those islands would offer if re-occupied by our forces. Each island is a veritable fortress, the assault against which cannot be contemplated unless the defences are neutralised, or reduced to a very considerable extent by prior action.'
The problem lay in the fact that 'prior action' meant either a naval gunfire bombardment or aerial bombing, with the very real risk of major loss of life among the British civilians still on the islands. Although most of the defences created by the Germans lay on or near the coast, the inaccuracy of bombing and shelling had the potential to pulverise two-thirds of Guernsey’s land area, and at least half of Jersey’s land area, and in that situation the casualty list among the 65,000 or so British citizens on those two islands would have been unacceptably high.
This complete series of operations was therefore cancelled, and the Channel Islands remained in German hands to World War II’s end.