Defence Electric Lights

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DEFENCE ELECTRIC LIGHTS (DEL)

Mark III DEL

Between 1890 and 1914 Defence Electric Lights were all under the control of the Royal Engineers. Responsibility for these Electric Lights subsequently passed to the Coast Artillery after World War I, who renamed then as Coast Artillery Search Lights (CASL).

Electric Lights had been used in warfare from 1853 but by the early 1970s the technology was beginning to develop sufficiently for effective deployment. The British Defence Electric Light was introduced in the late 1880s and the Manual of Electric Search-Lighting published in 1890 by the School of Military Engineering, Chatham. This is primarily a technical book but there is a brief chapter on the “Tactical Use of the Electric Light”. It is suggested that the electric light can be used not only to locate the enemy but also to prevent the enemy seeing you by obscuring his vision. The use of electric lights to locate an enemy is identified as:

A moving light to sweep an area. Search or sweep light.
A fixed beam across an area that the enemy must traverse. Fixed Beam.
By illuminating a distance rock or shoreline so that the enemy can be seen when they cross the light beam. Sentry Beam.

The light could of course be used both to cover sea approaches or a land front.

A copy of this 1890 Manual of Electric Search-Lighting can be seen here.

In 1902, the “Manual of Military Electric Lighting ” was published and this in turn was replaced by a new manual in 1909, “Military Electric Lighting ”. A copy of the 1909 manual on Military Electric Lighting can be seen here.

Between 1870 and 1880 a total of five Royal Engineer Submarine Mining Companies were established with mining establishments at:

Chatham
Sheerness
Gillingham
Gravesend
Portsmouth
Pembroke
Cork

Overseas Submarine Mining Establishments were established at Bermuda, Halifax and Malta.

By 1900 the Defence Electric Light has become a standard fixture to support coast defence batteries, submarine warfare defences and on land fronts such as the Victoria Lines in Malta.

ROLE OF DEFENCE ELECTRIC LIGHTS

The Role of the DEL was defined in these manuals as being:

Search Light to sweep and area to the front of the searchlight to detect any enemy movement withing this area. The majority of coastal defence DELs were this type of Fighting Light.
Fixed Beam Light or Sentry Light which covered a fixed area to its front. This could be to cover a boom defence, minefield, or road.
As a dispersed light with a broad strip of illumination to the front of a given location.

In the Coastal Defence role, the primary use of the DEL was to locate and then track the movement of any hostile vessel.

THE PROJECTOR

By the middle of the 1890s after some experimentation the British had settled on the 90cm light as the most appropriate for Coastal Defence Work. A common model was the Siemens Projector which had the following specifications:

Light Beam: Two Billion candles

Rang: 3,650 Metres

Method: 90 cm diameter carbon arc projector type using a parabola-ellipse reflector.

The light was created by the electric burning two carbon rods. Parts of these rods can still be found at some sites.

Click the images below to enlarge them.

ENGINE ROOMS

The Defence Electric Lights required electric power, and this required comparatively large engine rooms with one generator allocated to each Projector, with one generator as a back up. Initially steam power was used, but it took two to three hours to get up a head of steam, clearly to long if facing a surprise attack. By 1894 paraffin and oil was quickly adopted as an alternative and these generators only took two hours to become effective.

The Engine Rooms tended to be concentrated within forts and batteries in underground or casemated chambers for protection. Often, such as at Fort Carlisle in Cork, old heavy RML casemated positions were used.

Considerable importance was place on DELs and they were often placed under the control of a Searchlight Director Station (SLDS). This Directing Station was required to coordinate the use of the searchlights with the artillery gunners engaging any targets.

Click the images below to enlarge them.

DEFENCE ELECTRIC LIGHT EMPLACEMENTS

The DELs were initially mounted in simple rectangular emplacements with a single large window facing seawards. This window was fitted with steel shutters for protection. Entry to the position was usual from a covered way to the rear. By 1900 it was realised that the small aperture to the front of the building limited the arc in which the searchlight could be turned. The images below, click to enlarge, show examples of these early emplacements.

old_style_del_reenduff_battery_bare_island

The new design saw a more complex building with a large semi-circular front with steel shutters that could be moved back to the sides. A small radio room was also added, see plan below. The images below (click to enlarge) show examples of the later DEL emplacements. This basic design was to endure for half a century.

raised_del_emplacement_fort-st_rocco_malta

PROTECTING DEFENCE ELECTRIC LIGHTS

It was quickly realised that Defence Electric Lights were highly vulnerable to hostile fire. Various methods were adopted including:

The provision of steel shutters to cover the projector.
Attempts were also made to conceal lights in dead ground such as the fixed beams lights close to the shore line.
Adoption of the ‘Port Hole’ lens which was fitted over the front of the projector to give a concentrated beam. This allowed the light to pass through a narrow opening in armour plate before opening out again into a wider beam.
The see-saw searchlight which allowed the projector to remain covered in a bunker, with the light projected from a mirror on a beam that could be moved up and down. See images below.

The see-saw searchlight was tried out at various fortifications including:

Warden Point Battery, Isle of Wight
Fort Victoria, Isle of White
Chatham Lower Lines
Fort Paull on the Humber River
Fort Ballance, Wellington, New Zealand
Kings Bank Mine Field Battery outside Rangoon

They see-saw searchlight proved extremely hard to operate effectively in combat conditions and were not widely adopted.

Plan of See-Saw Searchlight

Fort Victoria, See-Saw Searchlight Emplacement

Official Plan,See-Saw Searchlight Emplacement

Prototype See-Saw Searchlight Position

DEFENCE ELECTRIC LIGHT MANUALS

The two manuals below are digitised by Google and can be downloaded by Members. They provide background information of Defence Electric Lights used between 1890 and 1910.

Manual of Electric Search-Lighting 1890

Military Electrical Lighting Vol. 2 1909

In the 1890s the Royal Engineers experimented with the Vertical Lift mount for defence electric lights. Very similar in layout to the see-saw searchlight but the arm was raised and lowered by a hydraulic mechanism. As far as is know the only position for this type of searchlight emplacement was the prototype built at Chatham on the Lower Lines.

It would appear that a searchlight was built underground by the Military Hospital, Georgetown in Bermuda. The light was on a ledge cut into a rock face. The light shone into the chamber to be reflected by a mirror on a turntable below. The light projected through a cut in the rock.

Defence Electric Lights