U-21 ran aground and was interned on 27 March 1940 after entering Norwegian waters. The government accepted navigational error as the explanation. The stronger suspicion here is that German submarine movements probably formed part of an effort to discover Norwegian patrol patterns and test border security. That remains an interpretation of the incident. Dozens of smaller diplomatic incidents added to the warnings that Norway occupied an important and increasingly contested position.
Notable Point · 1:02:02-1:03:24
U-21's internment and the warnings of German probing
U-21's grounding raised the suspicion that German submarines were probing Norway's defences, although the government accepted navigational error as the explanation.