The crop can’t get any smaller, but who is this?
Shes the C&HR's mallet, designed by Gresley himself.
I can't find the original lore post, so heres her lore
By the 1930s, the Chester and Holyhead mainline from Holyhead to Krestaen was overloaded. The railway's faithful class 5 2-8-0s rantheir goods trains as fast as was safe, but still struggled to keep up. Longer trains were not an option, as the existing trains already filled the passing sidings with mere feet to spare. The sidings could not be expanded without digging into cliffs along the line, which would risk landslides.Another route was needed. The existing mainline crossed the water at Holyhead onto Gwylan Island at Castell Hafan, then turned Northwest, climbing though farmland, plains, and forests in the heart of the Island before reaching the mountains. From there it climbed up the Llyn Pass to the capital, Krestaen. It was the clearest and best path to the city, but the path was narrow for long stretches in many places, taken up by the river Glaw. However, another line of the C&HR already came within 20 miles of the valley that held the capital city. A line ran North from Castell Hafan along the coast to the North Western port of Llanw.A path already existed between Krestaen and Llanw, and it would take minimal work to prepare it for track. Why then had the cities not already been connected then? Diawl's Bryn. The Devil's Hill. Climbing North, Northeast from the valley, the grade wound its way between the mountains with an average grade of 1 in 45 or 2.22%, in some places reaching 1 in 35 or 2.86% for short distances. For six grueling miles, the line climbed the mountain pass, before descending the 1 in 90 grade to Llanw. From there it was mostly flat running to Castell Haffan. It wasn't the steepest grade in Wales, nor the longest, but the combination was too great for the railway's existing fleet. The C&HR turned to May Traction and Railworks for an engine that could conquer the grade. A freight engine capable of making the run from Krestaen through the pass to Castell Haffan unaided. MTRW was forced to turn away the order, as such a monster was beyond their ability to manufacture. Next the C&HR turned to their mainland neighbor, the London, Midland, and Scotland Railway. The two railways had maintained a polite if distant working relationship since grouping, the the LMS running trains on the C&HR as far as Holyhead, and the C&HR running am express to London on LMS metals The LMS sent their number 4997, a 2-6-0+0-6-2 Garratt, for trials. While the engine certainly possessed the power required, the classes Achilles heel soon made itself known. The axle box design on the garratts was prone to hotboxes above 15 mph, far below the C&HR's running speed. Nonetheless, 4997 was purchased from the LMS to serve as banker until a suitable engine could be found. Several months later, a member of the C&HR board witnessed LNER U1 No.2396 banking at the Worsborough Incline . a 2-8-0+0-8-2, the U1 was the most powerful engine in Britain up to that point, and her frames were based on the LNER O4, the class the C&HR named the Class 5. The C&HR approached the LNER and its CME, Sir Nigel Gresley with their problem. The mention of the LMS's loan of 4997, and the subsequent chance to out-perform their rival, saw the LNER board order Gresley to design an engine capable of the task. Gresley spent a week watching the trains working Diawl's Bryn, before approaching the C&HR with his proposal. Rather than a Garratt like 2396, he wanted to design a simple mallet like those used in the United States. Whether Gresley truly believed a simple articulated was better suited for the C&HR than a garratt design, or if he simply wanted the chance to design such an engine is unknown; in either case, the C&HR approved the proposal. In Autumn 1933, Gresley presented the finalized design; a massive 2-6-6-4 locomotive which he dubbed the KM1.
Beyer Peacock was contracted to build the engine, and in early 1934, the KM1 left the works. With 6 cylinders and 76,000lbs of Tractive effort, she was the most powerful locomotive in Britain. She emerged in LNER Apple Green, shining in the morning light. The C&HR board, present to witness the unveiling of the engine, held a vote, and unanimously voted to name her Behemoth. Too large to travel by rail, she was delivered by sea to the harbor at Castell Haffan. Hundreds gathered to see the beast lowered onto the metals, even cold and with her fire unlit, she was an imposing presence. Two class 5 2-8-0s pulled her to Krestaen, where her fire was lit.A pair of American turntables had been purchased and installed at Krestaen and Castall Hafan in anticipation of her arrival, allowing her to be easily turned for the run to Castell Hafan. A line of 50 slate laden wagons waited as the engine backed down for her trail run, a pair of class 5's uncoupled at the back to bank the train in case of issues with the new engine. This would prove unnecessary. Behemoth charged the grade with a whistle, as was tradition on the C&HR, she was fitted with an American hooter whistle, and the echo thundered over the hills.the train had reached 30 mph when it reached the base, and the drivers of the two 2-8-0s eased their regulators, expecting the train to slow. To their shock, the train began to pull away from them, as Behemoth accelerated up the incline. They quickly caught back up, but kept having to increase the regulator as the monster at the front surged up the rails with a will. By the crest, Behemoth had broken 50mph, and the two bankers were left behind as she began the descent. Extra guard vans had been added to serve as extra braking power, but the C&HR had entrusted the 2-6-6-4 to a veteran engineer, and she skillfully kept the train in check. Behemoth would arrive in Castell Haffan ten minutes early to the cheers of the island's railfans. An order for a second engine was placed within the week, and Behemoth was soon joined by her sister Leviathan. Her arrival allowed 4997 to be sent to Beyer Peacock for a rebuild, emerging with new axleboxes, allowing her to join the two sisters on the run. By the advent of the second world war, the three engines were beginning to strain, so a third sister, Goliath, would be delivered in 1940. After the war, the facilities of MTRW would be expanded, and the C&HR would take delivery of a new Garratt design. Despite this, the three sisters would remain in service, keeping pace with the younger engines with ease.