The Royal Navy has confirmed that a torpedo was accidently "jettisoned onto the wharf" at Devonport Naval base on Wednesday.
However the weapon was a "dummy" device and there was no explosion or casualties.
In a statement the Royal Navy said: "We can confirm an incident occurred onboard HMS Argyll on Wednesday 12th March at 3.24pm, while the ship was alongside at Devonport Naval Base in Plymouth.
"During a training exercise, an inert Test Variant Torpedo (TVT) unexpectedly jettisoned onto the wharf. There was no explosion and no casualties.
"An investigation is now under way to determine the cause of the incident.
"HMS Argyll was conducting a system test when an inert Test Variant Torpedo was jettisoned unexpectedly. The torpedo is not an explosive hazard.
"The specific details of the incident are subject to further investigation and it would be inappropriate to comment further.
"A Test Variant Torpedo is a dummy weapon with no explosive content. There were no casualties involved.
"No one was on the jetty at the time of the firing The torpedo caused minor damage to an adjacent security fence (inside the naval base) where it landed.
"The result of the investigation will determine what actions will be necessary to avoid any repeat of this incident in the future. However, torpedo system test firing alongside in the naval base has been suspended subject to completion of the investigation."