Steam train enthusiasts will be able to take in the views of the countryside as the B1 class locomotive, 61306 Mayflower, chugs at a maximum speed of 75mph to Canterbury - the company's first ever destination.
The milestone falls on Wednesday April 8 and also marks the steam engine's inaugural trip on the main line for the first time in over 20 years, after being kept in 'exhibition' condition.
Brainchild and chairman of Steam Dreams, which operates The Cathedrals Express, Marcus Robertson, said: “Fifteen years ago, The Cathedrals Express set out from London on its first ever trip to Canterbury and a month later we made our second trip to Salisbury.
"To mark this special milestone, we are offering passengers the chance to travel between these two fabulous Cathedral cities.
"We are delighted to be returning to Hounslow and hope that locals will join us for what promises to be a very special occasion.”
Passengers will be taken back in time to experience the age of steam stopping at Hounslow at 10.40am before heading out across Kent, and into the beautiful cathedral city of Canterbury at 1.30pm.
The three-hour stop here will allow people to jump off and explore the historic city including a visit to England's oldest cathedral, dating back to 597 AD, and wander along the traffic-free high street discovering boutiques and specialist shops en route.
Passengers will re-join the Mayflower for the return journey at 4.30pm and will arrive back in Hounslow at 8.30pm.
Tickets for this celebratory trip are available in all four classes, ranging from £99 per person in Premium Standard with complimentary tea and coffee, through to the top class of Pullman Style Dining of £239 per person offering passengers a two course champagne brunch on the outward journey and a five course dinner on the return.
To book call 01483 209888 or visit the website.