The British Royal Navy aircraft carrier HMS Prince of Wales has broken down off the south coast of England shortly after embarking for exercises in the US.The 65,000-tonne warship left from Portsmouth Naval Base, Hampshire, on Saturday before an “emerging mechanical issue” occurred, dpa news agency reported on Monday.A Royal Navy spokeswoman said: “HMS Prince of Wales remains in the South Coast Exercise Area while conducting investigations into an emerging mechanical issue.”The vessel’s departure had earlier been delayed from August 26 because of a technical issue.The Royal Navy was not able to offer any further details or confirm if the earlier technical issue was related to the mechanical problem.