Summary
A Second World War ‘Blacker Bombard’ spigot mortar emplacement of around 1940-1941.
Reasons for Designation
The spigot mortar emplacement at RAF Kenley, Surrey, of around 1940-1941, is scheduled for the following principal reasons:
* Survival: the structure is well preserved, complete with ammunition lockers, pedestal and spigot;
* Rarity: this emplacement is a rare and early example of a fully intact emplacement, with a pentagonal plinth and a water sump;
* Period: spigot mortar emplacements were an important component of the nation’s Second World War defence policy including the defence of key fighter airfields and are therefore highly representative of this period;
* Documentation: the emplacement has been recorded during a recent archaeological investigation;
* Potential: the site has the potential to enhance our understanding of the construction, function, use and evolution of this type of defensive structure;
* Group value: with the designated assets at RAF Kenley, including the scheduled fighter pens (NHLE 1021242 and 1021243) and the Grade II-listed support buildings; officer's mess (1334947) and airmen's dining hall (1334946).
History
The Kenley Spigot Mortar emplacement was built around 1940–1941 as part of the anti-invasion defences for the airfield. Unlike the design in the official 1942 plan for such an emplacement which shows a round plinth, Kenley's has a pentagonal plinth.
Following the evacuation of the British Expeditionary Force from Dunkirk in 1940, Britain’s defences were strengthened against the very real threat of a German invasion. Diverse types of defensive structures were built in large numbers across the whole country, some of the most common including road and rail blocks, earthwork gun emplacements, barbed wire entanglements, anti-tank defences and pillboxes. These defensive structures were generally grouped, either at vulnerable or strategically important nodal points, around vital installations such as airfields, or arranged in linear defensive systems called stop lines, which were intended to obstruct the enemy advance.
One particular weakness identified in Britain’s defences was a grave shortage of anti-tank guns; 840 had been left behind in France following the Dunkirk evacuation and only 167 were available in Britain. Besides a lack of weaponry, the required ammunition was in such short supply that regulations prohibited the firing of even a single round for training purposes. A relatively cheap and portable solution to this problem was designed by Lieutenant Colonel Stewart Blacker of the Territorial Army.
Unlike conventional mortars, a spigot mortar does not possess a barrel, rather a steel rod, or spigot, is fixed to a base, with the projectile itself housing the propellant charge in its tail. When the mortar is fired, the projectile is pushed down onto the spigot, which explodes the charge and fires the round. The 29mm spigot mortar, or Blacker Bombard, was based on this premise, but with an inclined, swivel-mounted spigot and trigger firing mechanism. It was also fitted with a portable mounting consisting of four folding legs. The design for the Blacker Bombard dates back to 1939, although it was not accepted by the War Office until after the events of Dunkirk. The plan was submitted to the head of the Military Intelligence Research Department, Major Millis Jefferis, who was receptive to the idea, although other government officials initially opposed it.
Prime Minister Winston Churchill attended a demonstration of the weapon on 18 August 1940, and on his orders the weapon was put into full production. By mid-December about 8,000 of an initial order of 16,000 had been issued, and the initial order was increased to 28,000. Eventually nearly 29,000 were made. On 14 September 1941, the Directorate of Fortifications and Works (DFW) published drawing number 55280. This was an important development which introduced the designs for a pedestal mounting for the weapon, replacing the heavy folding legs with a fixed emplacement. By using these pre-prepared emplacements, the weapon could benefit from enhanced portability and stability, whilst still offering sufficient accuracy and protection for the crew.
The emplacement would normally comprise a concrete plinth thimble of approximately 1m diameter and 1m in height. A central steel pin would engage the underside of the weapon and form a swivel mounting. The thimble was to be centred in a pit about 1.2m deep giving access all around, with four concrete ammunition lockers recessed into the walls, each of which could hold 10 projectiles. A deeper approach trench was also included in the plan which was revetted with corrugated iron and pickets. A separate store building was often included for storage of the weapon and mounting when not in use.
RAF Kenley is built on the site of Kenley Common which is managed by the Corporation of London. It was converted for use as an aerodrome for the Royal Flying Corps in 1917 and enlarged through an Act of Parliament in 1939. The 800-yard runways and perimeter tracks completed in December 1939 (extended by a further 200 yards in 1943) and all of the fighter pens under completion in April 1940 have survived: this is an important survival, and one that relates to a military action of world historical importance.
At the end of March 1939, the Air Ministry had agreed to Sir Hugh Dowding's proposals for all-weather runways and perimeter tracks for critical fighter bases prone to waterlogging, mostly those in 11 Group in the south-east of England. In the following month it was agreed that fighter stations should have dispersals for three squadrons of 12 aircraft each, subsequent to which fighter pens with blast-shelter walls and internal air-raid shelters were erected on key fighter airfields: the designs, in which Dowding had taken a close interest since trials in August 1938, had already been established by Fighter Command Works.
Despite the demolition of the perimeter pillboxes in 1984, the survival, character and importance of Kenley's flying field as a well-preserved Battle of Britain site is thrown into sharper relief when it is realised that it was subject, on the 18 August 1940, to one of the most determined attacks by the Luftwaffe on a sector airfield, photographs of which - including an attack on a fighter pen - were afterwards printed in Der Adler magazine. During this raid, three personnel were killed and three hangars and several aircraft destroyed. 39 personnel were killed and 26 wounded on the 30 August, raids on the following day damaging the operations block.
Details
A Second World War ‘Blacker Bombard’ spigot mortar emplacement of around 1940-1941.
PRINCIPAL ELEMENTS: the monument consists of a circular emplacement visible as subterranean earthworks with exposed concrete structures (pedestals and ready-use ammunition lockers) and an approach trench.
DESCRIPTION: situated adjacent to the squash courts at RAF Kenley in an easterly direction. It comprises a sloping trench down to a polygonal pit, which is around 1m deep and 2.5m in diameter, finished with an earth floor. The sides of the pit are partially lined with four concrete ammunition lockers which are set back and alternate with concrete panels (some missing). In the centre of the pit there is a large pentagonal concrete plinth, roughly 1m in diameter with a curved top capped with a circular iron plate in the centre. This holds the steel pin or pivot, which extends approximately 10cm. A sump is set in the angle of the shelter trench and is the deepest part of the emplacement.
EXTENT OF SCHEDULING: the scheduled monument includes the known extent of the position along with a 2m buffer around the visible remains for their protection and management.
