725 has been a figment of my imagination for a number of years, not only as an enourmous, pull-anything locomotive, but as an inspirational powerhouse and a work of art.  2-10-2 has always been one of my favorite wheel-arrangements, So I simply took it and beefed it up Karnes-style.  The 725 first came roaring into my head around early 2000, when I was only seven.  She spent her days in sketches and doodles until, two years later, I took the engine and gave her a big bout of attention, resulting in a lot of development.  Since then, small modifications here and there have worked to make her perfect, still keeping her original looks, layout, power-generation and the trademark "Stack-fire".  I have made 725 truly my own engine, with all the little idiosyncrasies and odd features that I would come up with and put in, combined with realistic and sensible design.  Her little Karnes-Quirks include her red signal-mars-light, which is in constant use (because I find Mars-lights to be the coolest thing ever)  twin power genorators to supply electricity to an extra-long express train, five different whistles (one of which is a sliding tube)  both water and air pumps, an axle-driven waterfeed pump,  two different kinds of injectors, a vestibule cab, under-boiler-jacket sanding-lines, a combination of 6 of the driving-wheels being boxpok, the mid crank-driver being scullen, and the last two under the firebox being cast-spoked. Top this all off with a super-efficient and enourmous boiler built for burning bituminous coal and having a M.A.W.P. of 310 PSI, with a dual-Lempor exhaust arrangement.
Now, however, I am putting more and more effort into realizing this "Dream Engine" of mine in drawings, references and design diagrams, and in the far future, possibly a large-scale or even a live-steam working model.  
We shall start with the "History" of this locomotive and her journey through the years up to the present day.

725 had a humble beginning.  A contractor in California needed an immense freight locomotive to save the railway, and the boys down in Old Saybrook Connecticut were the ones to make it happen.  This engine would be one of the largest and most complex ever built save the U.P.'s big boy and challenger types, and certainly the largest and most complex ever built on the east coast.  She would have all the modern features save compound cylinders and a condenser.  
725 spent just six months on the drawing board, taking suggestions from the designs of the Nickel-plate Berkshires and several other successful locomotives.  Then, her ingenious and diligent team of designers and builders set to work and started to construct their massive creation.  Just after the flawless, immense boiler and running-frames were completed, Tragedy struck.  Across the country, the contractor and the railroad who 725 was being built for filed for bankruptcy, and the contract to build the great steam engine was both Null and void.  The project stopped dead, being bathed in oil and covered in tarps, her saddened, discouraged team of creators leaving her, having no further funding to continue their work.  
A year passed, and an Illustrious man working for the New Haven Railway came sauntering down to the shops one blustery day in January to see his friends, the builders of late, of the 725 project.  The sight of the immense boiler and frame assembly almost gave him a heart attack, stroke, aneurism, alsher and hemridge at the same time, and the first thing he asked when he woke up from his stupor was, "What engine is that?"
Promptly being obsessed with the completion of the engine and the prospect of having an unsurpassed one-of-a-kind experimental freight locomotive working for his railway, He promptly convinced the New Haven Railroad board of directors and superintendent to re-fund the project in their own best interest.  He also had his own personal agenda, he wanted to see the massive work of art brought to life, as he thought all steam engines deserved.
725 was back in buisseness, with an even bigger budget and the chance to run her on local rails near her shop of manufacture, the zealous workforce behind her when she first started returned to the shops with renewed morale and tools in hands.
This being 1947, the Old Saybrook workshops had more than adequate tools for making leviathan-sized steam locomotives.  For a year and a half, welders arced, trip-hammers clanged and rivets were driven as work progressed on the engine right on schedule.  She rolled out in steam in the spring of 1948 and immedeatly set to performing tests on the New Haven and New York Central Railroad lines.  She reached speeds of over 100 miles per hour, at the drawbar she could make a tooth-shattering 6013 horsepower and had an astounding, utterly un-heard-of tractive-effort of 119,751 pounds due to her heavy and even axle-loading.  
After a long and happy Career on the New Haven lines into the late 1960's, being well maintained and often called the pride of the line, steam was finally replaced with diesel power and 725, along with several others, was sent to the scrap-line. However, never once was she beaten by a diesel locomotive in any category, be it speed or drawbar-power.  To pull the kind of trains the 725 pulled, diesels had to be multiple-united in groups of five or six, and no diesel, even running light, could get close to the 725's 122.7 Mile-Per-Hour top speed, making her revered on most of the New England Railways up to the present day.
The scrap-line was hardly the end for such a fine engine.  Only a week after sitting on the line, She was spotted by an eccentric man of a great inheritance.  He insisted on buying the still perfectly operable locomotive and shutting her up in a storehouse indefinitely, until he could hire a crew to restore her to working order.  725 was shipped to the Seaport Marine warehouse in Mystic Connecticut, put under tarps, and forgotten.  Her "hired crew" never came, and her eccentric owner soon died when he buried his brand-new Ferrari in a cement retaining-wall.  

725 sat in the dust and gloom for many long years.
One sunny day, an un-suspecting Seaport-Marine shipyard worker came strolling into the warehouse, looking for a project.
He had been told there was quite a nice boat-hull sitting under the old beige tarp in the back of the building, suitable for work.
He was quite surprised indeed when he pulled the tarp off of a massive steam locomotive.
Having connections with the railroad, he brought over an inspection team from the Providence & Worcester Railroad, (who were scoffing, by the way.)
They were aghast to find a gargantuan steam locomotive, seemingly the only one of her type, that was in nearly perfect condition, needing almost no restoration whatsoever, her boiler filled with protecting oil, still having lubrication in her joints and still having soot on her firing tools, grates, ashpan and smokebox from her last run.
Laying tracks up to the warehouse, the workers did the only thing they could do, they simply would not overlook the locomotive's near pristine condition.  The engine was so large and heavy it was doubted that she could be towed out, so an FRA inspector was hired, and had an Aghast expression on his face when 725 passed every test and earned a boiler certificate with flying colors.   The ecstatic crew steamed the engine, and ran her down Amtrak Trackage back to her place of origin, old saybrook.  P&W workers and several railway enthusiasts, including the seaport marine worker who found her, suddenly became steam-locomotive volunteer-workers overnight, working to restore, refurbish, repair and replace the small pieces on the engine which needed it.  This comprised of mostly only lighting, external piping and fittings.  The hardest things to find, ironically and to the mirth of several, were spare moving parts for the mechanical mars-light, a special one-of a kind type made by the Pyle company specially for 725.  Help came from all over, The New York City Locomotive Works in conjuction with the Michigan, Frisco & Southern Central, The New England Museum of Steam and Wireless supplied several of the fittings, and the Mystic Seaport's machine shops made anything else the engine needed, including a lubricator, assuring their long-running high standard of complete historical accuracy along with perfect functionality.  
Anticipating rough conditions and treatment, 725's builders in old saybrook had poured their blood, sweat and tears into their engine and heavily over-built the boiler, namely the flues and crown-sheet, and had given her nearly double the amount of staybolts and plugs than was needed.  The New Haven Railroad was also very kind to the engine, the end-result being that the 725 needed no boiler repairs whatsoever, nor would need them for a long time to come.  
As soon as the locomotive was finished, instead of a preservation society being formed, 725 was put to work on it's very own division of the P&W Railroad, the "South Connecticut Freight Company."  To this day she is the only engine in the division, and surpasses diesels and electrics every day.  Many a time she hauls a regular express train or charter train for Amtrak, being a so-called part of their "Unofficial steam program".
She mainly shows her stuff when hauling triple-length freights for the P&W, or pulling trains for Amtrak when their diesels and electric units are experiencing problems.  
725 serves all of southern Connecticut from Mystic to Groton to New London to East Lyme to Old Saybrook to Essex to Westbrook to Madison to Guilford to East Haven to her old familiar line in New Haven.  Sometimes she ventures further west to Stamford on special occasions.  The group of men who run her are currently attempting to get 725 declared as a national historic landmark, being a truly one-of-a-kind American engineering triumph.