The tourist submarine was dropped into Lake Windermere in Cumbria where it will cruise the depths looking for wrecks as well as studying marine life.
The submarine, aptly named the Windermere, carries 10 passengers, and is the first to operate on the lake.
The manager of the Lakeside marina, Les Micklethwaite, said: "The locals will have been expecting something like the Trident, which is built across the way at Barrow. This will seem like a duck to them.
"But we think it will stir a lot of interest and it's a welcome addition to the steam cruisers we have here.
"The only other unusual craft we've had on the water was a Sunderland flying boat that stayed for one summer season."
The owners of the craft, Paul and Jane Whitfield, have successfully operated a submarine on Loch Ness.
Mrs Whitfield said of the venture: "I hope we will be here permanently. We are going to spend a week exploring the lake and then choose a couple of suitable sites from which to dive. We will ferry passengers from the lakeside out to the submarine.
"We'll be looking for wrecks and exploring areas that are little-known and in many cases never seen before.
"We think it will work very well, complementing the new aquatarium [marine- life centre] built here, and the steamers which cruise on the surface."
The submarine carries passengers and a pilot to a depth of almost 300 feet. It cruises at half a knot but can reach three knots when pressed. A single tour is likely to last an hour.
Mrs Whitfield added that marine life in Windermere was surprisingly varied.
"Fish life includes arctic charr, trout, pike, stickleback, perch and eels. And there have been numerous stories over the years concerning boat wrecks and sunken aircraft.
"The waters may be deep and dark but they will present little difficulty because our submarine is designed to operate at depths of 300 feet and is fitted with powerful underwater lights and large view ports.
"Sonar equipment, cameras and scientific instruments, help to locate and record any unusual targets."
The submarine will compete with an underwater walkway called "Tunnel With A View" at the aquatarium. It crosses the lake, allowing people to stroll among the boulders and pools, minnows and perch. Visitors will encounter stickleback, carp, stone loach and bullhead in their natural habitat. It also offers a fish-eye view of charr and pike, king of the predatory freshwater fish.