What annoys me is no where in education is it mentioned that the Channel Islands were invaded by the Germans. Pretty significant but never taught
That in itself is not entirely accurate. The Channel Islands were not defended at all (as they were deemed of no significant strategic value to the Germans), so no actual "invasion" took place, although the British, in their typical bumbling approach at the time, forgot to mention this aspect to the Germans, and so air raids killed about 50 Islanders, before they realised that the islands had been "de-militarised" and were undefended. Britain took the view of why waste more lives (of soldiers and civilians) in defending something of no actual strategic value.
The Germans used very much a "softly softly" approach to governing the islands, ( in very relative terms, obviously) and they were used for training and a "R & R" resort for tired soldiers from the eastern front. There was also a German penal colony there, the German Soldiers from which were put to work mending roads and building fortifications alongside other prisoners from other nationalities (mainly Polish, and some Spanish from the civil war) who were from the 4 or 5 Labour camps that were established there.
Many of the Germans left the islands soon after the invasion of Normandy, leaving a bit of a skeleton force there, but the islands were not liberated until after the German Surrender in May 1945. The last year of occupation was horrific, as many civilians died of starvation, as they were unable to be supplied by either the Germans or the Allies at the time, and were only kept supplied by a solitary Red Cross boat, that visited the Island about 4 or 5 times in 1944-45. The German garrison refused to surrender, even though their situation was hopeless.
Sorry, that went on far longer than I intended, but you are correct that it hardly gets a mention in History, because maybe the "establishment" is a little embarrassed by the whole affair, but at the time, they had very little option. There are loads of Books about the subject however, and a memorable ITV drama "Enemy at the Door"" which was very popular and aired in the late 70's.