Keen-eyed people walking past HMS Belfast recently will have noticed that there's not just one ship moored up, but two. Royal Navy offshore patrol vessel HMS Mersey is alongside the renowned London tourist hotspot to make a crew change.
However, unlike its historical counterpart, HMS Mersey is not open to visitors. Londonist got special permission to go aboard the ship, which patrols the English coastline 300-days-a-year acting as a deterrent and ensures fishing vessels stick to internationally-agreed quotas. You can see what it looks like inside, via the gallery above.
The ship is in the Thames until 7 October, when it will be pushed out backwards by tug boats, past Tower Bridge — which will be raised to get it through — before turning around and making the six-hour trip back to sea.
As it only comes to London about once a year, the visit means the crew has chance to indulge in some sightseeing, as well as allowing their families to come aboard — not normally permitted when it docks in Portsmouth, for security reasons.