The Cranwell branch was a 5.175-mile (8.328 km) long Logan and Hemingway built single track branch railway line that ran between Sleaford, on the Great Northern Railway, to the airship base at Royal Naval Air Service, Training Establishment, Cranwell, Lincolnshire (as RAF Cranwell was initially known). In addition to the main line, there were 2.4-mile (3.9 km) of sidings. It did not run via Rauceby station, as wrongly shown on the accompanying sketch.
Transporting materials and supplies to the RNAS Training Establishment along farm tracks was always difficult; a railway running parallel to Ermine Street from Ancaster was initially proposed, but severe gradients were found when surveying the route.
Matters were brought to a head by the harsh 1915-16 winter, which made the farm tracks almost impassable, resulting in a temporary railway track being laid from Sleaford. Following correspondence between the Admiralty and the Board of Trade early in 1916, work started on the permanent way later that year, after the Admiralty insisted that: "risks must be taken in wartime and work must not be held up in waiting for obligatory peacetime safeguards to be applied."
The line was in use by 1917, and a direct connection from the main up line at Sleaford opened up in March 1918.
In regards to finance, the line never broke even: in response to a Parliamentary Question, it was revealed that, even allowing for a credit in respect of the c.15,000 tons of Government stores that were transported along it during 1924, the line still made a loss of some £3,570. After coming under repeated pressure to reduce the deficit, the line ceased to carry regular passenger traffic in November 1926, with a consequent reduction in running costs. Its original use, for the conveyance of materials and provisions to the training establishment at Cranwell continued, however, together with the occasional passenger train (such as the special trains bringing public schoolboys to visit the college in the 1930s, the first Canadian contingent to arrive in the Second World War and the 1953 Flying Training Command Coronation contingent, which was pulled by a British Railways J6 class 0-6-0 tender engine with another of the Class on the rear).
From the sidings at Sleaford railway station, the route passed Sleaford West signal box, over the level crossing and then circled to the north, crossing the River Slea near to Drove Lane. It then proceeded up towards Leasingham, skirting Westfield Wood and entering the military base slightly to the south of the present road (B1429).
Five locomotives owned by the contractors Logan and Hemingway are known to have worked at Cranwell; these were all Manning Wardle 0-6-0 Saddle Tanks, with numbers: 3, 4 Epworth, 5, 7 Bletcher and 8.
A surviving Logan and Hemingway locomotive of the type used on the RAF Cranwell Railway (a 0-6-0 Manning Wardle saddle tank originally known as Number 10, but which now goes by the name of Sir Berkeley) is owned by the Vintage Carriages Trust.
The branch closed completely in 1956, the track being lifted the following year.
At May 2012, the original bridge over the River Slea remained in agricultural use, with that part of the track's route (leading from the bridge to Drove Lane) commemorated on an information board. The former Cranwell station building also remained in use, as a guardhouse.