In the second incident, a torpedo was accidentally launched from HMS Argyll inside Devonport naval base. The torpedo was an unarmed version used for testing drills, so did not explode when it impacted a safety fence. See the news story here.
In both cases, the investigations have been launched to try to understand the causal factors.
See our pages on incident investigation and common causes of human error to see how we are helping organisations manage the 'human factor' in their business.