Sounds interesting - What was it about international law that meant it didn't happen? I can't recall of any warships that were interned, but I have (I think) read of merchant ships being interned in World War II. In World War I, a number of German merchant ships were internded, including their fastest passenger liner, in the U.S. When the U.S. entered the war, they requisitioned those ships and used them as troop transports and supply vessels. Some of the ships had been rigged with scuttling charges in anticipation of seizure (the crew are either allowed to remain onboard, or be interned on land), but were found and removed before seizure.
The likelihood of a country entereing the war at some future point and the likelihood of of being on your side if they did, were factors in deciding whether or not to allow a ship to be interned or scuttled - two options that were a last resort. If the Graf Spee had of been interned, it may have been used by the Allies, as Uruguay entered the war on February 15th 1945. If the expense of repair had been deemed cost effective. No country is truly neutral
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