Built in 1926, the boat, called Xylonite, is featured in the Christopher Nolan movie with soldiers wading through the water to climb aboard.
And although it wasn't involved in the original evacuation, it was picked by the producers as a location because the interior and exterior are still perfectly in period.
Originally a sailing ship, it now has a motor, and is certified for sailing on the open sea. To take part in the filming, in fact, the 86-foot-long boat had to make it across the Channel - but is more usually to be found on a residential mooring at Limehouse Basin in East London.
Over the years, Xylonite has worked carrying cargo and giving boat rides to underprivileged children, but was sold to its present owners in 2011.
Since then, it's been thoroughly restored to create a four-bedroom home with nearly 1,400 square feet of living space. There's a whopping 28-foot living/dining room, with a wooden floor and panelling, and a fitted kitchen that's big enough for a range cooker and plenty of storage space.
The bedrooms are a surprisingly good size, and there's a traditional bathroom with claw-foot bath as well as a separate cloakroom. Above, there's a deck the full length of the boat.
The mooring costs around £875 a month, and while the owner will have to pay council tax, there won't be any stamp duty on the purchase.
Operation Dynamo involved the evacuation of 330,000 Allied soldiers from the beaches of Dunkirk in 1940 by a flotilla of yachts, pleasure boats and tugs - including 16 Thames sailing barges like Xylonite.
Dunkirk, starring Tom Hardy, Mark Rylance and singer Harry Styles, was released last month. And the owner of Xylonite even got to appear in the film as an extra, along with several of his friends.
10 best boatels around Europe
10 best boatels around Europe
Sleeps 4, from £134/night
Amsterdam is famous for its canals so why not make your visit even more authentic by living life on the water and staying in the Houseboat Suite Westertoren. This boat sleeps four and can be found right in the heart of the city, with views of the famous Anne Frank house and beautiful Westerkerk.
Sleeps 4, from £150/night
These two houseboats can be found in the heart of east London at Gainsborough Wharf. This is the perfect location for exploring the East End with Colombia Road flower market and Brick Lane both close by.
Sleeps 2, from £143/night
Salt and Sill is Sweden's first floating hotel and the property offers guests the chance to explore the beautiful Klädesholmen Island and Bohuslän Archipelago. The boatel is just 45 minutes drive from Gothenburg and there's even a seaside restaurant for guests to enjoy.
Sleeps 6 + 3 children, from £198/night
The Harbour Houseboat is moored in the scenic Bembridge Harbour with stunning sea views throughout. The boat is surprisingly spacious and is located just minutes from the village and beaches.
Sleeps 6, from £143/night
Although Larkspur is moored within walking distance of the city of Bath, you can take the opportunity while on board to explore the area on the Kennet and Avon Canal.The boat sleeps six and for those wanting to hit the water, you'll be taught how to handle and steer the boat before you leave.
Sleeps 2-8, from £27/night
These floating homes may not look like your classic houseboat but that doesn't mean they're missing any of the essentials. These quirky looking water properties boast terraces with views right over Lake Jamno. While some of the HT Houseboats are static, others are actually boats that can sail.
Sleeps 4 (2 adults and 2 children), from £176/night
If you fancy taking a unique opportunity while visiting Berlin why not try out the Modern Houseboat. With one side of the houseboat made almost entirely from glass, expect spectacular views of the water and surrounding area.
Sleeps 2, from £167/night
The Lilla Marras Reddingsboot is a former lifeboat that has been restored to make way for visitors. Guests can even hire their own private captain who will take you out on the water and demonstrate the boat's abilities.
Sleeps 4, from £79/night
Just a short walk from Sheffield's popular city attractions is where you can find this pair of stunning houseboats. The Houseboat Hotels. The 10-foot wide boats are surprisingly spacious and fully equipped with everything you need for a happy stay on the water.
Sleeps 8, from £252/night
This impressive property boasts four bedrooms and offers visitors the chance to relax while still in the heart of busy Paris. Devolu has a split-level deck, a terrace and even an ensuite bathroom.