In perhaps the most infamous case of friendly fire in the Second World War, the cruiser Mogami sank five friendly ships in one torpedo volley. This has become infamous in the modern day, as it's memed up and down the internet.

In fairness, it's the kind of story that seems impossible to believe for how unlucky it is. Unlike the myths around, say, Willie D Porter, however...

This did, in fact, happen. Embarrassing as it may be for the Japanese.

Further Reading:
http://www.combinedfleet.com/mogami_t...
https://www.amazon.com/Rising-Sun-Fal...
https://www.amazon.com/Japanese-Cruis...
https://www.amazon.com/Fleet-Gods-For...