This was brought up in several recent books and as a program on the History(?) channel too. The evidence is pretty thin. The Imperial Army was supposedly the developer in what is now North Korea. The island is inaccessable for survey for that reason.
There are no credible written technical documents that support the claim and the few eyewittnesses have very sketchy details of the event and little or no technical knowledge of it.
On the whole, it is unlikely.