It's a Medaille zur Erinnerung an den 13. März 1938 with Prague Castle bar.
From the images I have doubts about it being the real deal. The ribbon doesn't appear to be real and I'm not liking the bar. Wait for a few more opinions from those who have these in their collections but personally, I would look for another.
Looking for LDO marked EK2s and items relating to U-406.....
As Adrian said the hole set up is not looking good.
This is the medal for the Czechoslovakia, it is more refered to an annixation rather that an Anschluss as it was in Austrias case.