This is a London Midland and Scottish Jubilee Class locomotive. 191 of them were built between 1934 and 1936 and comprised the majority of the LMS express fleet. Such was the size of the Jubilee class that they were the largest express engine running on the lines out of St Pancras and pretty much monopolised the role.
Early models in the class suffered from superheating often leaving them short of steam but later modifications to the blast pipe and chimney helped to overcome this. Later modifications to the chimney were originally found on five of the class, this was a double chimney. In doubling up, the redesigned chimney offered a better airflow from the blast pipe, drawing a stronger pull of air into the furnace and improving the burn of the coal. This improved both the power and coal efficiency of the locos and would be fitted to this no 45596 Bahamas in 1961; which it retained through its withdrawal from use and into its recommissioning and preservation.
Power from the freely breathing engine meant a whopping 26,610 lb.ft of torque and a certified top speed of 75mph. Although as with many steam trains from the era, there's a chance it may have run faster. LMS was in direct competition with LNER while this train was in service, the two companies competing for luxury and speed from London to Scotland.
Of all the Jubilee Class locos made, only five survive to this day.